Fifth-seeded Flavio Cobolli rallied from two sets down to beat Francisco Comesana at the US Open on Tuesday, where top-seeded Alexander Zverev and No. 4 Coco Gauff were finally slated for first-round action.
Italy's Cobolli, runner-up to Zverev at the French Open, shook off an erratic start to triumph 3-6, 2-6, 6-3, 6-4, 6-4, dropping to his knees and raising his arms in celebration after closing out the four-hour, 13-minute marathon.
"In a Grand Slam it's never done," Cobolli said. "You have to fight to the last point."
Cobolli rallied from an early break in the fifth set, breaking back to pull level, breaking again for a 5-4 lead and sealing the triumph in the next game with a blistering forehand volley.
The Italian had been flailing in the first two sets against his 119th-ranked opponent, but he seemed to have turned a corner when he fought off two break points early in the third and broke Comesana with a powerful forehand for a 3-1 lead.
"After two sets down I went to the toilet and I changed everything because maybe (it was) unlucky," he told the crowd in an on-court interview. "So I changed everything -- and maybe it works."
Cobolli saved all eight break points he faced in the third set, including two in the final game, and roared to a 4-0 lead on the way to taking the fourth.
In the time it took Cobolli and Comesana to battle it out on the covered Louis Armstrong stadium, Americans Madison Keys and Taylor Fritz both posted wins on Arthur Ashe Stadium.
RYBAKINA RACES THROUGH
Meanwhile, players scheduled on outside courts waited through rain that delayed the start of play for almost four hours.
World number two Elena Rybakina, whose match on Grandstand court was one of those delayed by rain, raced past 17-year-old US wild card Thea Frodin 6-3, 6-2.
Rybakina, who claimed her second Grand Slam title at the Australian Open in January, is chasing not only a third but also Aryna Sabalenka's world number one ranking.
She showed no sign of the heel injury that forced her to retire from her quarter-final in Cincinnati this month, saving the only two break points she faced and breaking Frodin three times.
"We will see day by day," Rybakina said of the injury. "I'm glad I played the match, won the match. We'll see how I feel tomorrow."
She had praise for Frodin, ranked 585th and making her Grand Slam debut.
Although her competitive career is just beginning, Frodin's tennis talents were seen in "King Richard" the Oscar-winning film depicting Richard Williams and the rise of his daughters Serena and Venus Williams.
A 12-year-old Frodin was the stunt and body double for Demi Singleton, the actress who played young Serena.
"She played really well today," Rybakina said of the youngster, who peppered Rybakina with 11 aces, showed a tremendous serve but was prey to errors. "She has great shots, great serve. It was not easy."
Keys had to work harder, the 2025 Australian Open champion overcoming first-match jitters to beat 19-year-old Russian Alina Korneeva 7-5, 6-4.
In a match that featured 10 breaks of serve Keys squandered a match point in the penultimate game.
But she secured the victory with a break in the next, battling back from 15-40 down.
"It's always tough playing someone young and up and coming and they're going for their shots," Keys said.
"And it's so hard to play the first round of a Grand Slam," added the American, who crashed out in the first round at Flushing Meadows last year. "(You're) so nervous and wanting to do well."
Keys had plenty of time for those nerves to build with the tournament's Sunday start allow first-round play to stretch over three days.
Fritz meanwhile breezed to a 6-3, 6-2, 6-4 victory over fellow American Darwin Blanch.
Germany's Zverev, who followed up his maiden Grand Slam title with a runner-up finish at Wimbledon, will step on court at last on Tuesday night against 89th-ranked Italian Lorenzo Sonego while two-time Grand Slam champion Gauff faces Turkey's Zeynep Sonmez.