Roger Federer's return from a six-month injury lay-off suffered a setback when German teenager Alexander Zverev shocked the Swiss great 7-6(1) 6-7(4) 7-6(4) in an entertaining Hopman Cup tie yesterday.
The 17-time grand-slam winner underwent knee surgery last February and, after missing the French Open with a back injury, announced in July that he needed extensive rehab and would be sidelined for the rest of the season.
Representing his country in the mixed team event in Perth, Federer beat Briton Dan Evans on Monday but he faced stiff opposition from Zverev, 19, who enhanced his reputation by claiming his second win in three matches over the player many consider the greatest.
Elsewhere, top seed Serena Williams was knocked out of the ASB Classic in Auckland in the second round by fellow American Madison Brengle yesterday.
World No 2 Williams was beaten 6-4 6-7 (7/3) 6-4 by the 26-year-old, who is 70 places below her in the current rankings.
It was Brengle's first against a top-three opponent, with Williams making 88 unforced errors. "I really think I played - I'm trying to think of a word that's not obscene - but that's how I played," Serena said. Caroline Wozniacki eased into the quarter-finals after a 6-3 6-3 win over Varvara Lepchenko.