Roger Federer lost his first tiebreak this year before beating Arnaud Clement 6-2, 6-7, 6-0 as he began his title defence at the Nasdaq-100 Open on Saturday.
Women's champion Kim Clijsters suffered a shock, though, as she lost 7-5, 3-6, 7-5 in the second round to Jill Craybas.
Federer's victory enabled him to equal former world number one Pete Sampras's 19-match Masters Series winning streak. The Swiss began his run in Hamburg last year while Sampras's took place from Indian Wells to Stockholm in 1994.
The Swiss top seed seemed headed for a straight sets win against Clement but squandered a 4-0 lead in the second set tiebreak as he tried to close out the contest against the Frenchman who beat Rafael Nadal in Marseille last month.
Federer's uncharacteristic lapse saw him drop seven straight points as 53rd-ranked Clement forced a deciding set. It was the world number one's first loss in nine tiebreaks in 2006.
Federer quickly snapped back with a break at the start of the third set and quickly wrapped up the match as he earned his 23rd win of a season that so far includes just one defeat.
He will face German Tommy Haas in the third round after the former world number two beat Peru's Luis Horna 6-0, 6-3.
"This will be our third time this year," Federer told reporters. "He's coming back strong, it will be tough for me.
"He likes to play in the States, he almost grew up here. I have to watch out."
The Swiss pronounced himself neutral in his debut match with the HawkEye electronic line calling system, which malfunctioned for a minute during the contest but was quickly restored.
"We have umpires and linesmen to call the scores and see the mistakes," he said. "I'm neutral and want to see how it goes."
SHOCK DEFEAT
Second seed Clijsters of Belgium was joined at the exit door by her former fiance Australian Lleyton Hewitt, who lost for the first time in nine meetings with Tim Henman. The Briton ended the streak with a 7-6, 6-3 victory over the men's 13th seed.
Clijsters, deposed as world number one by Amelie Mauresmo on Monday, showed signs of rust as she played her first match since losing the Antwerp final to the Frenchwoman in February.
The U.S. Open holder committed 78 unforced errors against unseeded American Craybas and was broken six times during the two hour 15 minute contest.
"I wasn't consistent out there and had trouble finishing off the points," Clijsters told reporters after making her comeback following a recurrence of an ankle injury.
"I felt okay but I didn't play well. I must build up match toughness again.
"It's a disadvantage not to have trained as much as I would have wanted. You just want to forget this match as quickly as possible."
Last weekend's Pacific Life Open finalist Elena Dementieva, seeded sixth, defeated Anna Tatishvili 6-3, 6-1.
Success over Hewitt was sweet for Henman, who finally beat his nemesis for the first time in a rivalry which began on U.S. hardcourts in 2000.
MORE SATISFYING
Henman chalked up back-to-back victories over former world number ones, having beaten Marat Safin in the first round.
"I played a good match," Henman told reporters. "I think my match against Safin was much cleaner and of probably a higher quality but different conditions against a different opponent.
"This is more satisfying."
Since losing to American James Blake in the Las Vegas final earlier this month, Hewitt has won only once.
"The guys that come through that first match are obviously doing something pretty well to beat other reasonable players in the first round," Hewitt told reporters.
"Tim is definitely one of the tougher non-seeded players."
Henman's compatriot Greg Rusedski was eliminated 6-4, 6-4 by Argentine Juan Ignacio Chela.
