PARIS (AP) – Serena Williams entered Tuesday with a 37-0 record in the first round at Grand Slam tournaments.

She also began the day with a four-match losing streak, the longest of her career.

Williams focused on the second of those statistics, the more discouraging one. And while she never appeared truly in danger of coming out on the wrong end against 100th-ranked Klara Zakopalova, there were times when it did seem Williams simply could not wrap things up.

Twice, Williams served for the match and was broken. Eight times, Williams was a single point from victory and couldn’t complete the task. Finally, on match point No. 9, Zakopalova pushed a forehand wide to seal Williams’ 6-3, 6-7 (5), 6-4 victory, leaving the 10-time Grand Slam champion screaming and hopping at the baseline in a mix of joy and relief.

Whether it was the result of rust or a lingering knee injury or the swirling wind that carried debris from the stands onto the court, Williams’ mistakes kept coming. She finished with the same number of unforced errors as winners, 35, wound up wasting 13 of 20 break points and put only 55 percent of her first serves in play.

Williams called her performance “horrendous,” and said: “I just played junior tennis – or even worse.”

It was an anticlimactic end to a Day 3 that brought the first rain of the tournament, a two-hour-plus delay that interrupted easy victories for No. 5 Jelena Jankovic and No. 7 Svetlana Kuznetsova.

The only newsworthy upsets might not necessarily count as significant surprises, actually, given that they involved U.S. men losing to Argentines: No. 15 James Blake lost to qualifier Leonardo Mayer 7-6 (6), 7-5, 6-2, and No. 22 Mardy Fish was beaten by Maximo Gonzalez 6-3, 1-6, 6-4, 7-6 (4).

Bobby Reynolds lost in straight sets to No. 11 Gael Monfils of France, making U.S. men 2-7 in the first round.

Tuesday’s winners included No. 4 Novak Djokovic – whose opponent, Nicolas Lapentti, quit after hurting his ankle – No. 5 Juan Martin del Potro, No. 9 Jo-Wilfried Tsonga and 2003 champion Juan Carlos Ferrero.

Ferrero needed five sets to beat 2006 semifinalist Ivan Ljubicic, and while that and other matches might have interested fans, nothing going on around Roland Garros came close to the potential shock value of a loss by Williams.

Set aside, for a moment, that Zakopalova beat Williams on clay last month at Marbella, Spain, part of the American’s recent skid on the slow surface. Instead, consider this: The Czech player is 7-24 at Grand Slam tournaments.

“I feel very disappointed,” Zakopalova said. “She’s Serena.”

Well, yes, she is, but she didn’t play like Serena for long stretches Tuesday, including when she fell behind 3-0 in the second set. Right after that, though, Williams won five consecutive games – including 10 points in a row – to go ahead 5-3.

Seemingly back in control, Williams slipped again into sloppy play.

“It just happens,” she said. “It shouldn’t happen at my stage in my career, but it did.”

In the next game, Williams wasted five match points, including a marvelous 32-stroke exchange that ended when she sailed a forehand wide as the pitch of her grunts rose by an octave at a time.

Still up 5-4, still a game from victory, Williams double-faulted and was broken.

“I probably should have closed it out,” Williams acknowledged, “but I just didn’t, and I couldn’t.”

An errant forehand by Williams capped the tiebreaker and sent the match to a third set, where she held three more match points with Zakopalova serving at 5-2. But with Williams playing tentatively, Zakopalova erased those three chances, too, then broke to 5-4.

By now, the crowd at Court Suzanne Lenglen was backing the underdog, chanting “Kla-ra!” and giving Williams a hard time when she’d question calls.

“They don’t really pull for me a lot here,” Williams said. “That’s fine.”

Eventually, she came through, gritting her teeth and dealing with those spectators, her own shaky play, her balky knee, the 50-degree weather, the upset-minded opponent. Some might figure this showing portends trouble in Paris, but Williams’ father – who also coaches her – took an optimistic view.

“I don’t see trouble. What I see is a champion that found a way to win on a day that she didn’t play good,” Richard Williams said. “See, in order to be a champion, you have to win when you should lose.”