John Millman has made a successful start to his title defence at the Astana Open in Kazakhstan.

The Australian No.2 overcame local qualifier Dmitry Popko 3-6 6-1 6-4 in Nur-Sultan to advance to the second round.

Millman was surprised in the first set by a player ranked 140 places below him at No.188, but came back to win in two hours and nine minutes.

The fifth seed trailed 2-0 in the deciding set but again showed his fighting spirit to claw his way to victory and a move on to a showdown with Spaniard Juame Munar.

"I am hoping I can build on that match," Millman, who won his one and only ATP Tour trophy at this event last year, said.

"It was a little bit scrappy from my end.

"Credit to my opponent, he came out having played a couple of matches in those conditions and was probably a little bit better from the start.

"Once I found my feet, I felt a little bit more comfortable."

Millman's compatriot Marc Polmans, who had fought his way through qualifying to the main draw, lost to teenage Italian Lorenzo Musetti 4-6 6-2 4-6.

"It was a really tough match, but I played well," Musetti said.

"He was really solid and he was not missing a ball, so it was not easy to (win) the point.

"In the third set, I broke him in the third game, a really tough game, and that game was a turning point of the match. So I am really happy with the win."