Roger Federer suffered a setback in his preparation for the Australian Open as teenager Alexander Zverev secured his second successive win over the Swiss master at the Hopman Cup in Perth.
Rising star Zverev, who is ranked 24th in the world at the age of 19, got the better of Federer last June in a semi-final at the Gerry Weber Open in Halle.
And the young German again proved too strong for the 17-time grand slam singles champion on Wednesday, edging a tight encounter that saw all three sets decided by tie-breaks.
There were only two breaks of serve in the match - both in the first set - but Zverev came good when it mattered most to prevail 7-6 (7-1) 6-7 (4-7) 7-6 (7-4).
Former world number one Federer is making his return to action in Australia this week after six months out with injury and comfortably beat Dan Evans on Monday in his opening singles match.
His defeat to Zverev left Switzerland 1-0 down in their match against Germany - with Belinda Bencic facing Andrea Petkovic ahead of a mixed doubles match later in the day.