PARIS—Anyone who’s felt that Serena Williams needed to be tested at this French Open, either for her own sake or for the sake of the WTA’s reputation, got their wish on this bright, cool, and sometimes blustery day.

Hitting a wall after she roughed up Svetlana Kuznetsova in the first set, Williams struggled mightily before she put all the scattered pieces back together again to win the quarterfinal match with her fellow former champion. Once again, when the chips were down, Williams flipped them back over and survived a risky undertaking in two hours, 6-1, 3-6, 6-3.

But those scores also point toward the true nature of this clash, which is that it wasn’t as close and competitive as it may appear. That’s because the shifts of momentum and form in this were obvious, dramatic, and somewhat artless. It wasn’t until the very last few games that both women managed to play at a high level at the same time.

You can pretty much throw the first set of this one out the window. Williams fought off two break points in the very first game and then swiftly broke Kuznetsova at the first opportunity with a drop shot winner. It was off to the races for the top seed, as she rolled to a 3-0 lead and soon thereafter 5-2. The winners poured off her racquet, while Kuznetsova struggled to keep the ball in the court.

That first set lasted just 28 minutes, but Kuznetsova must have been over-hydrating because she took a bathroom break as it ended. Has there ever been a match in which the winner had to take a bathroom break after a first set? These breaks last unconscionably long; my own feeling is that they ought to put a port-a-potty right on the court (incorporate it into the umpire’s chair?); who needs this gamesmanship?

Anyway, the momentum shifted drastically upon the resumption. Kuznetsova held with ease and broke Serena without even having to play a deuce—thanks to a Williams double fault at 30-all followed by a backhand error off a serve return. Kuznetsova did a good job holding a lead despite the break point Williams earned in the next game, and she broke again for 4-love. Now, it was errors streaming off Williams’ racquet, while Kuznetsova found her range. Her inside-out forehand was especially deadly at this stage of the match.

Williams return ensures that no service game is safe, and she did manage to break Kuznetsova twice in the next three games. But Williams also was broken in that string. She managed a solid hold to claw back to 3-5, at which point I probably wasn’t the only one thinking she might slash her way to the straight-sets win. But despite falling behind love-40 when she served for it, Kuznetsova managed to reach the safety of deuce (thanks to two Williams errors and a second-serve ace) and, in short order, serve out the set.

That had to be a sobering moment for Williams, who looked to be in big trouble. She made just eight winners while clubbing 13 unforced errors in that second set. And at the start of the third it looked as if she might not be able to withstand the heat Kuznetsova was applying. Williams’ timing seemed off; even her serve and return lacked sting. She was broken in the first game of the deciding set with a pair of errors, one forehand, one backhand. When Kuznetsova held for 2-0, the situation looked grave for Williams.

Then came the second, massive shift of momentum—and the most important game of the match.

Williams won a five-deuce game in which she stared down three break points. The second of those chances for Kuznetsova was the best point of the match. After a long rally, Williams hit a stiff and tentative smash that Kuznetsova retrieved, and after the ensuing scramble, the Russian just missed the sideline with a drop shot. Williams got out of that game with an inside-out forehand winner so powerful that Kuznetsova, wrong-footed, fell over as she barely got her racquet on the ball.

Williams was back in the hunt at 1-2; her savage cries of “Come on” only confirmed it. Was anyone really surprised that, after that critical hold, she broke Kuznetsova as if she were a dry stick?

Although they were theoretically dead even at 2-2, Kuznetsova’s game began to crack. She did earn a break point in the next game, but blew it thanks to a forehand error. Two more miscues by Kuznetsova enabled Williams to hold, and from 3-2 the American broke serve once again.

There were some good points played over the final three games, but Williams would not be headed. The ending was short and sweet, as Williams rolled to 40-15 in the final game and ended it with a cross-court forehand drive from just behind the service line.

Stat of the Match: Williams hit 37 winners—18 more than Kuznetsova was able to produce.