Carlos Alcaraz and Daniil Medvedev moved quietly into the third round of the US Open on Thursday while big-hitting American John Isner delivered his trademark stack of aces in taking his final bow at Flushing Meadows.

Alcaraz entertained a record crowd at Arthur Ashe Stadium with a 6-3, 6-1, 7-6 (4) win over Lloyd Harris but the match also revealed a lack of sharpness which the Spaniard will need to rectify if he is to successfully defend his US Open crown.

Some dazzling shot-making from Alcaraz had the crowd on its feet but he also piled up 29 unforced errors and showed a lack of concentration at key moments.

After the match Alcaraz focused on the positives, rating his effort as “great” but admitting to a letdown in the third set.

“I think I played great, a great match,” assessed the Spaniard. “But obviously in the third set, he started to play better. I got down a little bit. I needed extra energy in the third set.

“In the end, I think I played a pretty good match and will try to keep the same level.”

The 20-year-old will need to improve with rival Novak Djokovic on the prowl for a 24th grand slam and seeking revenge for his Wimbledon loss to the Spaniard.

Medvedev survived a late-night fright before taming Australian battler Christopher O’Connell 6-2, 6-2, 6-7 (6), 6-2.

After strolling to a two-set lead, Medvedev had looked headed for routine passage. But O’Connell tapped into the energy of the crowd.

With chants of, “Aussie, Aussie, Aussie, Oi, Oi, Oi” rising from the stands, O’Connell dug in to take the third set to a tiebreak when a shaky Medvedev double-faulted to hand him a well-deserved third set.

In the end, the third-seeded experienced Russian needed all his resolve to push O’Connell to the exit.

Isner, the standard bearer for American men’s tennis during some barren years, never made it past the quarter-finals in 17 US Opens but his towering presence and booming serve made him a crowd favourite.

He signed off his professional singles career with a 3-6, 4-6, 7-6(3), 6-4, 7-6 (7) loss to fellow American Michael Mmoh, but did not go quietly, adding 48 more aces to his record total.

Along with his thundering serve, Isner is remembered for winning the longest professional tennis match in history against Frenchman Nicolas Mahut at Wimbledon in 2010, which lasted 11 hours and 5 minutes and took place over three days.

There will still be plenty of American content in the third round as third seed Jessica Pegula romped to a 6-3, 6-1 win over Romania’s Patricia Maria Tig and Madison Keys, the losing finalist in 2017, enjoying a 6-1, 6-2 win over Belgian Yanina Wickmayer.

The British charge at the US Open will carry on without 2012 champion Andy Murray, who was outclassed by Bulgarian Grigor Dimitrov 6-3, 6-4, 6-1.

Known for his grit and warrior spirit, the 36-year-old Scotsman appeared to have little left in the tank on a broiling Arthur Ashe Stadium court and had no answer to the 19th seed’s firepower.

“I was expecting, honestly, five sets,” said Dimitrov. “He’s a tremendous competitor ... I’m very happy with the fight.”

Women’s second seed Aryna Sabalenka dished out more pain for British fans by knocking out Jodie Burrage in straight sets.

But it was not all bad news as 16th seed Cameron Norrie, 26th seed Dan Evans and Jack Draper, with a 6-2, 6-4, 7-5 upset of 17th seed Hubert Hurkacz, moved onto the third round.

Tunisian fifth seed Ons Jabeur, looking to return to the final and atone for last year’s loss to Iga Swiatek, is through to the third round but was made to work hard by Czech teenager Linda Noskova before sealing a thrilling 7-6 (7), 4-6, 6-3 victory.

Russian Daria Kasatkina battled back to defeat American Sofia Kenin 2-6, 6-4, 6-4 and reach the third round.

The 13th seed looked to be heading out of the tournament after Kenin cruised through the first set and took a 3-1 lead in the second. But she settled in from there to launch a comeback.

Ukrainian Elina Svitolina came from behind to beat Anastasia Pavlyuchenkova of Russia 5-7, 6-4, 6-4 in a high-quality match.

Svitolina sent down her 10th ace on match point to end the nearly three-hour clash to the delight of the supportive crowd at Louis Armstrong Stadium.