Four-time champion Novak Djokovic beat Philipp Kohlschreiber but had trouble closing out a 7-5, 7-5 win on Tuesday to power into the fourth round of the Indian Wells Masters to join Rafael Nadal as a winner.

The world number one bidding for a third straight trophy at the Tennis Garden defeated his German opponent for the eighth time in nine meetings.

But it was no easy win, with Kohlschreiber saving four match points in the ninth game of the second set to pull within striking distance 4-5.

Djokovic eventually came through with a break to take victory but was not pleased with his level.

"This should not happen to a professional, it was totally my fault.

"I had errors on three match points in a row. Philipp is an experienced player and he took advantage to come back to the match."

Djokovic escaped to stand 18-1 this season, with his only loss coming in last month's Dubai quarter-finals where he retired against Feliciano Lopez with an eye infection.

Nadal took revenge for a grand slam loss against a dangerous Spanish rival, winning 6-0, 7-6 (11-9) over Fernando Verdasco.

The fourth-seeded Spaniard will find himself facing an entirely different kind of challenge in the next round when he plays switched-on German teenager Alexander Zverev.

The number 58 has ridden a Californian explosion of form, cementing his latest success with a comprehensive 6-2, 6-2 thrashing of experienced French 16th seed Gilles Simon.

Nadal had an easy time in a runaway opening set against Verdasco, who humiliated the former number one with a first-round Melbourne knockout in five sets two months ago that reverberated through Nadal's game during a poor February.

That upset was the third for Madrid's Verdasco over his previous four meetings with with his Mallorcan rival. Nadal won the first 13 times they played.

Nadal made sure he was not caught out again as he swept the opening set and battled in the second. Verdasco, ranked 65th, missed on three set points in the second set and two more in the tiebreaker before Nadal advanced on a second match point.

"I played a great first set, very good quality of tennis," Nadal said. "No mistakes. That's important for me, serving very well, returning very well.

"I had some mistakes in the beginning of the second, especially with the serve, distracting my concentration, distracting my confidence. I was suffering at the end of the second set.

"Normally in this kind of match I have more to lose than him, so he's able to play very aggressive. I felt lucky to win the tiebreak. It was an important victory for me."

Nadal posted 18 winners while Verdasco was weighed down by 38 unforced errors and had his serve broken five times.

The 18-year-old Zverev needed just 67 minutes to school Simon, beating the Frenchman for the second time in five weeks on the back of five breaks of serve.

"I thought I played really well today, I was really aggressive and hit a lot of winners," Zverev said. "Beating someone like Gilles 6-2, 6-2 is something that gives me a lot of confidence."

"I was really ready for a long fight and a long three-set match," he added. "I'm really happy that I got through so quickly."

Japan's fifth seed Kei Nishikori advanced over American Steve Johnson 7-6 (8-6), 7-6 (7-5) while ninth seed John Isner turned in a home win, beating Adrian Mannarino of France 6-4, 7-6 (7-4).

The winners meet next for a spot in the quarter-finals.

"It's tough to expect great tennis here," Nishikori said of the notoriously windy conditions at the desert venue. "But I thought I was patient today."

"Obviously it's not easy, but I have been playing good tennis these two matches and having confidence winning today, too. So I'm looking forward to playing the next match," he said.

French seventh seed Jo-Wilfried Tsonga put out American Sam Querrey 6-3, 6-4 while US ninth seed John Isner beat Adrian Mannarino 6-4, 7-6 (7-4). Austrian 11th seed Domenic Thiem eliminated Jack Sock 7-5, 6-7 (5-7), 6-1.

In the women's fourth round, Serena Williams motored past Kateryna Bondarenko 6-2, 6-2 while third seed Agnieszka Radwanska defeated former number one Jelena Jankovic 6-3, 6-3 and eighth-seeded double Wimbledon winner Petra Kvitova overcame American Nicole Gibbs 4-6, 6-3, 6-4.

Kvitova said she needed a wake-up call after dropping the opening set. "I was like, 'Okay, so today I want to play long.'"

"But that's how it is. The first set, I had a break but I still didn't play what I wanted. In the beginning of the second set until the end I think I played a really good game," she said.

Fifth seed Simona Halep, the defending champion, advanced when Czech Barbora Strycova quit trailing 6-3, 1-0 with a fever. Compatriot Karolina Pliskova beat Briton's Johanna Konta 7-6 (7-2), 3-6, 6-3.

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