Australian world number 30 Nick Kyrgios fought back to beat Pierre-Hughes Herbert at the US Open after an apparent pep talk from the umpire.

Kyrgios was a set and 0-3 down to his French opponent when official Mohamed Lahyani climbed down from his chair during a changeover.

“I want to help you. This isn’t you. I know that,” Lahyani said.

Krygios went on to win 4-6 7-6 (8-6) 6-3 6-0 and could play world number two Roger Federer next.

Swiss Federer, a five-time champion at Flushing Meadows, is playing France’s Benoit Paire for a place in the last 32.

Kyrgios claimed after the match that Lahyani was concerned about his medical well-being rather than his motivation in their on-court discussion.

“He was just concerned about how I was playing – he was like: ‘Nick are you OK?'” said Kyrgios.

“I was like: ‘Yeah everything is fine.’ I just wasn’t feeling great.”

The 23-year-old won 19 of 25 games after the exchange and the incident sparked debate online.

Kyrgios, who hit 25 aces in his first-round win over Radu Albot, delivered the joint-fastest serve of the tournament so far with one 142mph tee-off.

Elsewhere world number four Alexander Zverev advanced to the third round for the first time with a comprehensive win over France’s Nicolas Mahut.

The 21-year-old German won 6-4 6-4 6-2.

Fourteenth seed Fabio Fognini fell victim to Australian John Millman, losing 6-1 4-6 6-4 6-1.