World number one Novak Djokovic was beaten 6-4 6-4 by Bernard Tomic but Serbia recovered to earn a 2-1 win in their Hopman Cup Group A match against Australia in Perth.
Djokovic was under pressure from the start of the men's singles, saving five break points in the opening game before Tomic eventually earned the break in the ninth game for a 5-4 lead.
The 20-year-old served out the first set and that pattern was repeated in the second, Tomic breaking in the ninth game and then closing out the match on his own delivery.
"I played a very, very good match and I'm just happy after the training the last few months, that it's all coming good and the training's paying off," said world number 52 Tomic, who was mired in a slump for most of 2012.
"Hard work does pay off. I'm still improving but I feel this today was a very good sign. I've got to continue playing like this."
Djokovic conceded that Tomic deserved his victory, saying: "He played really well. He deserved to win. I knew I was coming here to Australia really late and it still takes time for me to get used to it.
"But I'm not taking anything from his win. He played terrific. He's in great form. I was always on the back foot and he was the better player."
Serbia turned things around to remain unbeaten at the mixed team event; Ana Ivanovic beat Ashleigh Barty 6-2 6-3 in the women's singles before Ivanovic and Djokovic teamed up to for a 6-4 6-7 (8-10) 10-6 win over Tomic and Barty in the deciding doubles.