Juan Martin Del Potro continued his promising return from an 11-month injury layoff by beating top-seed Fabio Fognini 4 6, 6-2, 6-2 to reach the quarterfinals of the Sydney International.
The second-round triumph over Fognini further demonstrated the Argentine's return to top form ahead of next week's Australian Open.
The former number four needed a wildcard to gain entry to the main draw as his world ranking had dropped to 338 during his lengthy absence. He showed the benefit of concerted preparation by beating Fognini in one hour, 48 minutes.
The Argentine's quarterfinal opponent will be Kazakhstan qualifier Mikhail Kukushkin, who upset sixth seed Pablo Cuevas 7-5, 7-5.
Second-seed David Goffin of Belgium also suffered a second round loss, going down 6-3, 6-3 to Italy's Simone Bolelli.
Fourth seed Julien Benneteau of France beat Vasek Pospisil of Canada 7-6, 6-3.
On the women's side, defending champion Tsvetana Pironkova beat Barbora Zhalavova Strycova 6-4, 6-1 to stay on track to win the tournament for the second-straight year as a qualifier.