Novak Djokovic's golden ATP Cup run has come to an end after Serbia suffered a 2-1 loss to Germany in their winner-takes-all tie in Melbourne.
Djokovic had earlier kept Serbia's title defence on track with a spirited three-set win over German star Alexander Zverev.
The 6-7 (3-7) 6-2 7-5 victory over seventh-ranked Zverev levelled the tie at 1-1, and meant it would all come down to the doubles.
Djokovic teamed up with Nikola Cacic for the deciding rubber, but they went down 7-6 (7-4) 5-7 10-7 to Zverev and Jan-Lennard Struff.
Preparing his quest for a ninth Australian Open crown, world No.1 Djokovic vented his frustrations in the second set of the doubles loss by breaking his racquet.
The result booked Germany a semi-final berth against Russia.
Struff had put Germany 1-0 up in the decisive Group A tie with a 3-6 6-3 6-4 win over Dusan Lajovic in the opening singles rubber.
Struff's victory put the heat on Djokovic, but the 17-times major winner responded to improve his record in the teams' event to 11-0, including nine singles victories.
"It was a great match. I thought we both played well. He definitely had a big serving match," Djokovic said after his singles win.
"It was so difficult to play against him today, missiles from the other side of the court, both first and second serve.
"He was going for it and not too many double faults, so you've got to give him credit for being courageous and trying his best.
"In the last couple of games you could see that both of us were quite tight."
Zverev threw his racquet up high in celebration after winning the doubles, but the mood was far different after he lost his singles match to Djokovic.
"I was quite frustrated actually that I lost the singles because I thought I had the chances," he said.
"I could have done better. I thought it was a really good match, especially for how early it is in the season.
"Once I got to the locker room, it's obviously the captain's decision and everyone else's decision, but if they needed me on the doubles court I was ready to play."
Italy are through to the semi-finals after topping Group C with wins over Austria and France.
Russia secured a semi-final berth after accounting for Japan and Argentina in Group D.
Spain clinched Group B honours after Pablo Carreno Busta, deputising for injured world No.2 Rafael Nadal, defeated Michail Pervolarakis 6-3 6-4.
Carreno Busta's victory made it impossible for Greece to overtake Spain even if they won Friday's tie.
Greek star Stefanos Tsitsipas at least built some confidence ahead of Monday's Australian Open start with a 7-5 7-5 win over Roberto Bautista Agut.