The No. 5 seed from Thailand has won 15 of his last 17 matches -- all on hard courts -- including his victory at Long Island and runner-up showing at Washington, D.C.
"I lost to Safin twice before. They were very close matches," Srichaphan said. "This time I picked it up and corrected it. I just tried to hold my serve and play solid from the baseline."
Safin, the 2000 U.S. Open champion, reached the final at the Australian Open in January and the semifinals at Roland Garros, but has yet to win a title this year.
Srichaphan will play third seed and two-time finalist Yevgeny Kafelnikov of Russia in Friday's semifinals.
"He's a tough player," Srichaphan said. "I am expecting a good match. I lost to Kafelnikov at Wimbledon in the second round in 1999."
Pushed to three sets in his previous two matches, Kafelnikov rolled past sixth-seeded Ivan Ljubicic of Croatia, 6-3, 6-2. The 28-year-old Russian has won three matches in a row for the first time since capturing his lone title of the year at Halle in July.
"I have played three matches in a row. They were all very tough matches," Kafelnikov said. "With my every win here, it is the best preparation for the Davis Cup (semifinal next week). There is no substitute for playing real matches. Every victory and intensively hard match I play is extremely important for my confidence."
Belarussian qualifier Vladimir Voltchkov advanced to the semifinals when second seed Tommy Haas retired with a right elbow injury. Voltchkov was leading, 6-2, 2-1, when the German decided he could no longer continue.
"It was better for me to stop," Haas said. "My elbow was hurting every shot I made. My injury has been going on for a while now. It started with my shoulder and now it's compensating with my elbow. You could say it is something serious. I have to go back to Germany now to my doctor and see what's going on."
The ailment flared during Wednesday's match against Sargis Sargsian and became progressively worse during practice and the match against Voltchkov.
"I hope it won't effect my schedule for the rest of the year," Haas said. "I have been kind of used to it, but sometimes it just gets too much. I hope I will be fit enough to play Davis Cup (qualifying) and then the rest of the tournaments I have entered for the winter."
Voltchkov is just 5-3 this season, but won a grasscourt challenger in Manchester earlier this year. A Wimbledon semifinalist two years ago, the 24-year-old Belarussian has found it difficult to bounce back from a rotator cuff injury.
No. 8 Davide Sanguinetti, staying on track for his third title of the year, rallied past Denmark's Kristian Pless, 4-6, 7-6 (7-1), 6-2. Sanguinetti won in his native Italy February when he captured the tournament in Milan and beat Pless en route to his second title of the year in Delray Beach in March.
"He started playing really well," Sanguinetti said. "He was playing two shots and then producing a winner. In my mind, if he kep playing like that, I would shake his hand and say well done because he was playing better than me. I knew he couldn't keep up this level. Sooner or later he would drop the level of his tennis."