Jack Draper reached the round of 16 at the Madrid Open after opponent Matteo Berrettini retired injured as play resumed following a nationwide power cut.

Play was suspended on Monday in the Spanish capital after the electronic line-calling system and scoreboards went down.

Power was restored to the venue on Tuesday morning, allowing fifth seed Draper to take on Italian Berrettini, who is ranked 30th.

Draper won the opening set 7-6 in a tie-breaker after 57 minutes, finally converting his third set point opportunity.

At the end of the set, Berrettini withdrew from the match after speaking to Draper, indicating he had an abdominal problem.

"He said his abs were pulling," Draper said of Berrettini after the match. "Credit to him for coming out here and putting on a good first set.

"In general, Matteo is a very positive player. So it's always tough to see a friend having an injury. I know it's plagued him a lot."

Draper will face American Tommy Paul in the last 16.

Earlier, Grigor Dimitrov converted his third match point - over 24 hours after his first - to beat Jacob Fearnley and reach the quarter-finals.

The match was suspended during Monday's outage with Dimitrov leading 6-4 5-4, and they resumed their match on Tuesday after Iga Swiatek's battling three-set win over Diana Shnaider.

Bulgaria's Dimitrov eventually beat the 23-year-old Briton 6-4 7-6 (7-3).

Fearnley had to serve to stay in the match when play began and, despite a double fault, did well to keep Dimitrov at bay.

World number 16 Dimitrov had a second match point at 6-5 on the Fearnley serve but the Scot saved it to eventually force a tie-break.

Dimitrov promptly took control of the breaker and won the last five points in a row.

He sets up a meeting with Canada's Gabriel Diallo, who beat Britain's Cameron Norrie.

Diallo, who only qualified for Madrid as a lucky loser, came from behind to beat Norrie - ranked 91st in the world - 2-6 6-4 6-4.

There was an upset on Tuesday evening as men's top seed Alexander Zverev was beaten in straight sets by 20th-ranked Francisco Cerundolo.

Argentina's Cerundolo won 7-5 6-3 to reach the quarter-finals, with Germany's Zverev failing to convert a single break point.

Earlier, defending women's champion Swiatek won her ninth successive match in Madrid with a 6-0 6-7 (3-7) 6-4 victory over Russia's Shnaider.

Poland's Swiatek was not at her best, committing over 50 unforced errors, but she saved 11 of the 13 break points she faced to get the edge over Shnaider.

She will face Madison Keys - who beat her in the Australian Open semi-finals on her way to a maiden Grand Slam title - next after the American's 6-2 6-3 victory over Donna Vekic of Croatia.

World number one Aryna Sabalenka also progressed to the last eight with a straight-set victory over Peyton Stearns, beating the American 6-2 6-4.