Andre Agassi had to rally past hard-serving Australian Mark Philippoussis, 4-6, 6-3, 6-2, on Tuesday night.
Williams hit 31 winners, broke serve 8-of-16 times, and had her way at the net. Although she needed 61 minutes to eliminate Bartoli, which is longer than normal for her, Williams maintained the match was tougher than it appeared.
"I think the score line wasn't true to the match at all," she contended. "She played really well. I definitely had to work hard to win that match. I knew I was going to, because I had seen her play before."
Although Bartoli felt like she could handle Williams' groundstrokes, she was unable to deal with the power of the overall package.
"When she hit in the baseline, her ball is not too quick," Bartoli, 18, said in broken English. "I feel I can play every time, and I feel I can run her. When she runs, she's definitely not very good, so ... When the rally beginning, I was quite confident in my shot, but when I serve, and she come to the court, I say, 'Oh, my God. Oh, my God, what going to be happening?' I was going just to serve and, boom, (she would) return winners. I serve, (she would) return winners."
Williams has dominated since her triumph here last season. She has won four straight Grand Slams and five other events in the last 12 months.
Other than her sister Venus, one of the few players to challenge Williams has been Kim Clijsters, who setup a semifinal encounter with a 6-2, 6-0, victory in a tidy 53 minutes over No. 9 Jelena Dokic of Yugoslavia.
"These are the matches you really look forward to," Clijsters said. "These are the matches, when you're younger and you're practicing and you're working hard, these are the matches you dream of."
Clijsters beat Serena Williams in the final of last year's season-ending tournament in Los Angeles, but squandered a 5-1 lead in the final set of the Australian Open in January.
She has been a legitimate No. 3 behind the Williams sisters, has won two tournaments, including the Tier I Indian Wells, and has reached at least the semifinals six times in as many events.
"I feel like I'm a lot more consistent than what I was about a year ago, maybe two years ago," Clijsters said. "I knew then that my best level was the same as what it is now, but if I went a little bit under my best level, I dropped a whole lot. Now I feel like I'm consistent throughout. Even if I'm not playing my best tennis, I still feel that I'm capable of playing well enough to beat a lot of girls."
Meanwhile, after dropping the first set to Philippousis, Agassi went on to extend his winning streak against the talented Aussie to six matches.
"You never feel in control against Mark," said Agassi, who is nursing a sore right shoulder that caused him to miss Indian Wells. "He takes the match in his own hands on so many shots. I needed to step up and I did on some crucial points."
Agassi, 32, is seeking his third straight title at Miami and sixth crown there overall. He has won 15 consecutive matches at Miami.
Marcelo Rios, whose promising career has been stunted by injuries, pulled out of this event for the second straight year because of a back injury.
This Tennis Masters and Tier I event awards $500,000 to the men's champion and $393,000 to the women's winner.