INDIAN WELLS, United States (AFP) - World No. 1 Roger Federer finished off Federico Delbonis in a rain-disrupted match on Sunday (March 11), to reach the third round at the Indian Wells tennis tournament as five-time champion Novak Djokovic was toppled.

The Swiss legend returned to stadium court on Sunday afternoon and needed an hour to close out his second-round victory 6-3, 7-6 (8-6).

"It's been a long time since I have been interrupted at night and have to come back the next day," he said.

His title defence got off to a soggy start on Saturday night when play was suspended because of rain showers with Federer up a set and tied 2-2 in the second.

The clouds rolled in just before the start of their match on Saturday and after a short delay to start the first set, they managed to play until the skies blackened and the heavy rains came in the second. After another 90-minute delay, the organisers suspended play for the night.

Federer, who has a record 20 Grand Slam singles titles, is making his 17th appearance in the California desert and is assured of remaining world No. 1 if he makes it to the semi-finals.

He extended his 2018 win streak to 13 matches and has only dropped three sets from 34 played this year.

Federer hit five aces and won 74 per cent of his first-serve points in the match which took a total of one hour and 41 minutes over the two days.

He will face 25th-seed Filip Krajinovic in the third round.

Federer and 10th seed Djokovic both came into the tournament seeking to become the first six-time winner of the event.

But Djokovic fell at the first hurdle with a shock loss to Japanese qualifier Taro Daniel, who sent the out-of-sorts Serb tumbling with a hard-fought 7-6 (7-3), 4-6, 6-1 victory.

It was another snag in the return for world No. 13 Djokovic, who admitted he lacked composure while playing in just his second event of 2018 and first since having surgery.

'Very weird'

Djokovic said it felt like the "first match I ever played on the tour". "I mean, I just completely lost rhythm, everything," he said.

He is making a cautious return to the ATP Tour after stopping his 2017 season following Wimbledon due to a right elbow injury. He lost to Chung Hyeon in the Australian Open fourth round in January before undergoing the surgery.

Djokovic scrambled to win the second set on Sunday but the rust from the layoff was evident as he made 62 unforced errors overall.

He had four aces but served poorly overall, making four double faults.

Federer said he understands well how even a champion like Djokovic could be struggling to find his game so soon after having surgery.

"To me, it's not that surprising," Federer said. "When you go away from the game for over a two-month period, it starts feeling a little bit that way.

"When you do come back from injury or when you haven't played in a long time, it just takes extra effort.

"It is still early stages for Novak coming back and the first one after surgery. He's only going to get better from here."

Daniel, who is ranked 109th in the world, advanced to the third round where he will face Gael Monfils of France.

In other men's matches, Juan Martin del Potro steamed his way into the third round as the sixth seed needed just 69 minutes to beat Australian teenager Alex de Minaur 6-2, 6-1.

Argentina's del Potro, who is fresh off winning the Mexican Open title in Acapulco, hammered five aces and broke de Minaur's serve five times.

The win sets up a third-round showdown with Spaniard David Ferrer, who defeated Tennys Sandgren of the US 6-2, 7-6 (7-3).

World No. 3 Marin Cilic also won on Sunday, defeating Hungary's Marton Fucsovics in straight sets, 7-5, 6-3.