Sampras advanced to his third straight U.S. Open final with a 7-6 (7-5), 7-6 (7-4), 6-2 victory over Sjeng Schalken of the Netherlands.
Agassi knocked out top seed and defending champion Lleyton Hewitt of Australia, 6-4, 7-6 (7-5), 6-7 (1-7), 6-2.
The American greats have met 33 times, with Sampras having won 19 of those matches and three of their four Grand Slam final confrontations. He defeated Agassi in their last two encounters, including last year's fantastic U.S. Open quarterfinal, 6-7 (7-9), 7-6 (7-2), 7-6 (7-2), 7-6 (7-5).
"It will be just a huge moment for both of us, for the game," said Sampras, who beat Agassi for his first career major here in 1990. "Two older players, two rivals over the years. He brings out the best in me. To walk out there with him is very unique, very special."
Their first Grand Slam clash occurred here in 1990. Sampras was the unassuming 19-year-old who upset Ivan Lendl and John McEnroe to reach the championship match while Agassi was the tour's brash budding superstar with long multi-colored hair and denim shorts.
At the time, Agassi had reached the semifinals the previous two years and was runner-up at the French Open earlier in the season but suffered a 6-4, 6-3, 6-2 defeat in the final.
"I couldn't be more thrilled about (the final)," Agassi said. "You always question if it will ever happen against.
"You have a career that you spend playing your best tennis against one of the greats of all time, and you're never guaranteed even with the best of careers, to have that sort of rivalry and that sort of opposite that brings out the best in you over the years.
"This is less about what we pull out of each other tomorrow, more about a nice toast to the past. It's going to be a great day."
Agassi trails, 3-5, in Grand Slam encounters with Sampras. He won their 1995 Australian Open final and a five-set thriller in the semifinals at Melbourne two years ago. But Sampras cooled off a red-hot Agassi in the 1995 U.S. Open championship match.
"I've played some of the most meomorable matches of my career against Pete, coming out on both sides," Agassi said. "We're opposite in everything we do. Out on the court, we're two styles that are going against each other. It allows for many aspects of the game to kind of reveal themselves. And it's exciting to play against it, because every point, something special seems like it can happen."
The participants in Sunday's final will be the oldest at the U.S. Open in the Open era. Both Sampras and Agassi will be vying to become the oldest winner here since 1970, when Ken Rosewall captured the crown at 35.
Sampras became the first man to reach three consecutive finals here since Ivan Lendl completed his stretch of eight in a row from 1982-1989. With his eighth championship match here, he tied Lendl for third on the all-time list during the Open Era (before 1968).
"The years of domination are over, but I still feel like I can win a major," said Sampras, 31. "I still believe that. If I didn't believe it, I wouldn't attempt to play."
A win Sunday would give Sampras five U.S. Open crowns, tying Jimmy Connors for the most in the Open Era.
Defeated in the final the last two years by younger foes, Sampras has more than 24 hours to rest for his match against Agassi, the sixth seed.
Schalken came back from a love-40 deficit in the first game and later owned a set point in the first-set tiebreaker. In the second, he twice was two points from the set, but could not overcome Sampras' huge serve.
"He was just serving so good that I just couldn't get them on my racket because he was placing the ball so good with 120 miles an hour serves," Schalken said. "I couldn't touch the ball."
Sampras notched the match's first break of serve in the fourth game of the third set. He faced his only break point in the seventh game but saved it with an overhead.
After his 13th double fault, Sampras hit a service winner before blistering his 23rd ace to go ahead, 5-2. He broke Schalken again to complete the win in two hours, 24 minutes.
"I take my chances. My serve is my weapon," Sampras said. "I'm going to use it whenever I can. I get burned sometimes when I go for too much, and I throw in some doubles. But if I'm going to lose out there, I want to do it on my terms, not being conservative."
Sampras has been tested throughout the tournament, but remarkably has rediscovered the form that made him the all-time leader in major titles with 13. He struggled through a five-set match in the third round with Britain's Greg Rusedski, who later suggested that Sampras has "lost a step and a half."
The next day, Sampras showed no ill effects from the five-setter as he raised his level of play to defeat third seed Tommy Haas in four sets. On Thursday, he made it look even easier with a straight-sets rout of rising American star Andy Roddick.
"I think the Haas match was a tough match to get through. I played pretty well," Sampras said. "Roddick, I peaked there for a while. Just kind of carried on through the weekend."
Holding his lowest seeding for a Grand Slam at No. 17, Sampras has not won a title in more than two years. He has gone 33 events without a victory after his record-setting triumph at 2000 Wimbledon, the 63rd of his career.
"I've never felt like an underdog," he said. "It's been 10 years since I felt that way. I still feel like when I step out against any of these guys, I'm the favorite to win. Maybe not on paper, maybe not in a lot of people's minds, but in my heart I still believe I'm the one to beat. But I haven't shown that this year."
Sampras improved to 5-0 lifetime against Schalken, who turns 26 on Sunday. The 24th-seeded Dutchman was playing in his first career Grand Slam semifinal.
Schalken stayed in the match with well-placed serves and backhand passing shots.
"I don't have that big game. I have to think a lot on the court," he said. "I have to play a lot of shots to get my service game. I don't have that killer serve, so that's a big disadvantage."
The day's second match was as frenetic as the first was measured. Hewitt's hustling style has caused Agassi problems in the past and the reigning Wimbledon champion led in the first set, 4-2.
"Every time we've played, it just always feels like such few points separate each set," said Agassi, whose coach Darren Cahill worked for Hewitt last year. "He had many chances up there. He was up a break early in the first, served for the second.
"I should have closed out the third, but that's the way a match is going to go with a guy like Lleyton and with a game like mine, because we're both taking good cuts at ball after ball. And you just can't get discouraged when maybe the tide turns a little bit on you."
Hewitt jumped out to a 3-0 lead, but Agassi won six of the next seven games to take the first set.
The American again fell behind a break to start the second but immediately broke back and leveled the set at 2-2. Hewitt, showing his fleet feet and his unparalleled retrieval skills, forged ahead, 5-3.
However, the Australian could not close out the set, committing the second of double faulting for the second time on break point in the ninth game.
In the tiebreak, Agassi won possibly the point of the tournament to take a 2-1 lead. He hit a drop shot from the baseline that Hewitt hit for his own drop shot.
Agassi barely returned it with a forehand that Hewitt put behind his opponent. Agassi reached back to flick the ball over the net. After Hewitt's backhand volley went right to him, he smacked a swinging forehanded winner.
Agassi went ahead, 5-2, but Hewitt kept on running down shots, pulling the tiebreak level. However, he hit a backhand wide and concluded a long rally with a forehand into the net to fall two sets down.
The 21-year-old Australian rallied from an 0-3 deficit in the third set, evening things in the eighth game. He broke for a 6-5 lead, but Agassi won the 12th game with a wicked, running crosscourt forehand winner. Hewitt won the lopsided tiebreaker, 7-1, as Agassi appeared tired.
But the former world No. 1 had enough left to break for a 3-2 advantage. He repelled a break point in the next game and broke at love for a 5-2 lead. Agassi gained triple match point with his seventh ace of the match. Hewitt saved two with two forehand winners, but hit a backhand into the net.
Hewitt had his match winning streak against Americans snapped at 23. The top seed has not claimed the championship here since Sampras won in 1996.
"I could have been easily up two sets to one, rather than two sets to one down," Hewitt said of his missed opportunities. "I felt like I was starting to get on top in the fourth at 2-1, love-30. I felt like I was starting to get another chance there. To his credit, he came up with four big points then."