Osaka won 6-3 4-6 6-2 to defeat the 35-year-old Romanian, who was playing in her final Australian Open before retirement.
A fuming Cirstea stormed away from Osaka after a brief handshake at the net, before turning around to exchange words with the former world No 1.
Naomi Osaka walks onto court.
Osaka was baffled by the confrontation and brought it up immediately during her on-court interview, although she was not directly asked about the incident.
Asked what it took to advance to the third round, Osaka replied: “Apparently a lot of ‘come-ons’ because that’s what she was angry about.”
It drew a mixed reaction from the crowd and Osaka added: “I mean, I tried to play well. I think I made a lot of unforced errors but I tried my best. She’s a great player. I think this was her last Australian Open, so, sorry she’s mad about it.”
Cirstea appeared to be frustrated by Osaka pumping herself up between serves and when this was pointed out, an exasperated Osaka replied: “She could have asked me.”
Meanwhile, record-breaking Stan Wawrinka battled through a five-set epic to reach the third round and extend his final Australian Open by another match.
The 40-year-old wildcard, who will be retiring at the end of the season, defeated the French qualifier Arthur Gea 3-6, 6-3, 3-6, 7-5, 7-6 (10-3) in four hours and 33 minutes – the longest match of the tournament so far. He became the second-oldest man to win a match at the Australian Open since it moved to Melbourne Park with a three-hour, 19-minute battle over Laslo Djere on Monday.
Switzerland’s Stan Wawrinka celebrates after winning his second round match against France’s Arthur Gea.
The Swiss, a three-time grand slam champion and former Australian Open winner, went the full distance, requiring a match tiebreak to defeat Gea on a raucous Kia Arena. According to Opta, it was the 49th five-set match of Wawrinka’s career at the grand slams, which moves him past compatriot Roger Federer for the most in the Open era.
He is also the oldest man to reach the third round of the Australian Open since the great Ken Rosewell in 1978, who was 43.
Wawrinka forced the fifth set with a trademark one-handed backhand winner down the line, a shot that had the Kia Arena on its feet after the former world No 3 found himself two sets to one down. In a wild fifth set, both players had multiple chances to break, while Gea required timeouts for medical treatment and to fix a broken shoe.
The drama continued into the fifth-set tiebreak as the 21-year-old Gea, making his Australian Open debut, began to cramp. After Wawrinka won a 21-shot rally to establish control of the tiebreak, Gea doubled-over in cramp before serving. Wawrinka then produced a miraculous lob from behind the baseline, which finally broke Gea’s resistance.
Wawrinka required a wildcard to enter the Australian Open main draw, with his ranking down at 139th in the world before the tournament.