Bernard Tomic's commitment to tennis is expected to come under the microscope again after the Australian pulled out of his first round match in Acapulco citing "unbearable heat".

Tomic lost the first set to American Donald Young in a tiebreak but looked disinterested and lethargic at stages before withdrawing from the match.

The loss ruled out a potential second-round clash in Mexico with compatriot and sixth seed Nick Kyrgios, who downed Israel's Dudi Sela 3-6, 6-3, 6-3.

Tomic's withdrawal without apparent injury appears more questionable given the temperature in Acapulco was 27 degrees at the time - a far cry from the heat in places like Melbourne Park which can reach into the 40s.

He had also made the final at the same venue in 2016 where he comfortably played through five matches, eventually losing a tough three-setter to Austrian Dominic Thiem.

It continues an ordinary start to the season for the former world number 17, who has now lost three consecutive first round matches.

He's slid down the rankings to number 41 and with the clay-court season ahead - where he's consistently struggled - it is hard to see his situation improving in the short term.

Tomic has had a history of retiring from matches and pulled the pin during four ATP fixtures in 2016.

He also infamously holds the record for the fastest loss in ATP tournament history, going down to Finn Jarkko Nieminen in just 28 minutes back in 2014.

AAP