Britain's Andy Murray was forced to dig deep before beating promising Czech Jiri Vesely in the third round of the BNP Paribas Open at Indian Wells on Monday.
The Wimbledon champion won 6-7 (7-2) 6-4 6-4 but only after clawing back from the brink of defeat against the 20-year-old Vesely.
Murray lost the opening set despite going up an early break but then struggled on serve against the left-handed Vesely, ranked 77th in the world.
The Scotsman was broken six times in the match and trailed in both the second and third sets but fought back each time, reeling off four consecutive games to seal victory.
"It was just one of those matches where there wasn't one period where I thought that the level of tennis from both of us was high at the same time," said Murray.
"That can create a lot of breaks and a lot of sort of back and forth swings in the match. It wasn't just the start of the match that was frustrating. The whole match was."
Murray will play either Canada's Milos Raonic or Colombia's Alejandro Falla in the next round as he bids to win one of the few North American hardcourt titles to have eluded him.
Switzerland's former world number one Roger Federer also advanced after a tough workout on Monday but the 32-year-old said he was satisfied with his performance.
Federer, the four-time champion, was pushed all the way by Russia's Dmitry Tursunov but won two tiebreaks to triumph 7-6 (9-7) 7-6 (7-2).
Federer, who won his 78th career singles title in Dubai, play either German Tommy Haas or Japan's Kei Nishikori in the fourth round.
"I feel like I'm in a good place," said Federer. "I know what my solid level is. Even if I won 6 and 6 today, I just feel like I was calm and served for the set.
"Okay, got broken. Still managed to stay calm. Down ... in the second; stayed calm and came back. So those are the moments where you feel there is confidence around somewhere."
China's Li Na, the top seed in the women's draw, had no problems booking her place in the fourth round, easily beating Karolina Pliskova of the Czech Republic 6-3 6-4.
Despite dishing up nine double-faults and having her own service broken twice, Li was far too strong and streetwise for Pliskova, wrapping up the win with an ace.
"At least I could win the last point and stay in the tournament," Li said.
"If you're a tennis player, you'll make double faults. At least I can improve my serve even more from here."
Li is looking to win her first Indian Wells title and continue her great start to the year after capturing the Australian Open.
Her next opponent is Canada's Aleksandra Wozniak, who defeated Russia's Anastasia Pavlyuchenkova 6-1 6-7(3-7) 6-0.
(Reporting by Julian Linden in New York; Editing by Frank Pingue/Greg Stutchbury)