Two sets into his delayed second-round singles match on Monday night, social media was abuzz with pending upset alerts.

It appeared, after uninspired 6-3, 6-3 setbacks, that sixth-seeded Felix Auger-Aliassime of Montreal was going to become the second major upset of the 2023 Australian Open.

But Alex Molcan, the 25-year-old Slovakian singles star, sputtered and then collapsed, as Auger-Aliassime stormed back with spirited 6-3, 6-2, 6-2 victories to avoid an early exit at Melbourne Park.

Auger-Aliassime, who struggled out of the gates in the first round before bouncing Vasek Pospisil of Vancouver in four sets, started even slower against Molcan, but appeared by the fourth set to have run his rival out of gas.

"I had belief in myself after winning the third set. I had come back before and I felt I could do it again. But boy, it was a difficult day," said Auger-Aliassime, who finished with 23 aces in the match that took three hours and three minutes to complete.

A clearly hurting Rafael Nadal lost his second-round match to Mackenzie McDonald 6-4, 6-4, 7-5, abruptly ending his title defence and bid for a record-extending 23rd Grand Slam trophy.

The 35-year-old Spaniard pulled up awkwardly at the end of a point late in the second set against the 65th-ranked McDonald.

The No. 1-seeded Nadal was visited by a trainer on the sideline, then left the court for a medical timeout and treatment on his hip. Up in the stands, his wife wiped away tears. Nadal returned to play, but was physically compromised and not his usual chase-every-ball self.

All the matches on Monday night were delayed by four to seven hours due to heavy rains and slippery courts.

Bianca Andreescu of Mississauga, Ontario, who waited almost 6 1/2 hours to play Cristina Bucsa (book-suh) of Moldova in her second-round singles match at the Australian Open, didn't waste much time getting down to business, winning the first set 6-2 in 29 minutes. But Bucsa battled back to win the second set 7-6 to set up a winner-take-all third set. Bucsa would go on to win that set 6-4 to advance to the third round against the top-ranked Iga Swiatek (EE-guh shvi-AHN-teck) of Poland.

Andreescu defeated Marie Bouzkova 6-2, 6-4 of Czechia in the first round of the Open, while Busca bounced Eva Lys of Ukraine 2-6, 6-0, 6-2.

Denis Shapovalov of Richmond Hill, Ont., was still waiting to play his second-round match against Taro Daniel of New York when Andreescu's match ended.