Defending champion Juan Martin del Potro came from a set down to dump top seed Fabio Fognini out of the Sydney International and advanced to the quarter-finals on Wednesday.
The Argentine Grand Slam champion has won his first two matches in 10 months at the tournament following wrist surgery as he fights his way back to the top echelon of men's tennis.
Del Potro, a one-time world No.4 but whose ranking has dived to 338 due to his inactivity, defeated the world No.18 Italian Fognini 4-6, 6-2, 6-2.
"I thought I played better. I feel better on the court, especially in the end of the match," said del Potro, who defeated Ukraine's Sergiy Stakhovsky in Tuesday's opening round.
"I serve well, I hit good forehands, and my backhands improved from yesterday to this match a little bit.
"I need to keep playing with these guys, hitting the ball as fast I can and keep trying.
"My wrist is the same. It's not getting worse, so I have confidence with that. Of course I'm very happy to beat my first top 20 player of the year."
The Argentine is playing in the Sydney tournament on a wildcard for his first event since last February following an injury-ravaged 2014 season during which he had surgery on his left wrist.
Del Potro grew stronger through the match after receiving treatment on his wrist from the trainer in the opening set, and he looked close to his best form in the deciding set to eliminate Fognini.
Del Potro played down concerns over the treatment he received from the trainer on the court.
"I'm feeling okay. It was nothing dangerous. Because I sweat too much and the tape goes out, but nothing special," he said. "It's like spray to keep the tape on."
The former US Open champion will meet Kazakhstan qualifier Mikhail Kukushkin, who upset Uruguayan sixth seed Pablo Cuevas 7-5, 7-5 in the last eight.
Second seed David Goffin also followed Fognini out of the tournament, after losing to Italian Simone Bolelli.
Bolelli downed the Belgian 6-3, 6-3 and next faces Serbian qualifier Viktor Troicki in the last four.
Troicki eliminated Spaniard Pablo Andujar 4-6, 6-3, 6-3.