Novak Djokovic defeated Lleyton Hewitt 6-2, 6-4 Tuesday to help Serbia remain unbeaten at the Hopman Cup with a 2-0 victory over Australia.

Ana Ivanovic stopped Alicia Molik 6-4, 6-0 to win the first point for Serbia despite appearing to hyperextend her left knee in the second set. Djokovic and Ivanovic later combined to win the doubles against Hewitt and Molik 6-7 (5), 6-4 (10-6 tiebreaker).

Serbia can reach the final Saturday with a win Thursday over Belgium, which eliminated Kazakhstan 3-0. Seven-time Grand Slam winner Justine Henin downed Sesil Karatantcheva of Kazakhstan 6-4, 6-3.

Henin, who is returning from an elbow injury sustained at Wimbledon, made her first appearance at the Hopman Cup.

"I wait 28 years to come here, but maybe I'll come back next year, who knows," she said. "I love to play in Australia, they have a sports culture, it's just great."

Djokovic, who has won his last four matches against Hewitt on the ATP Tour, saved four break points at 2-2 and won four games to take the first set.

Cheered by a pocket of noisy Serbian supporters, the third-ranked Djokovic broke Hewitt in the second game, only for the Australian to break straight back. The next games went with serve until Hewitt double-faulted twice at 5-4 to hand Djokovic the win.

"I played great, especially the beginning of the second I was playing some of the best tennis I've played in this year and a half," Djokovic said. "We players have great respect for him (Hewitt) because he's a big fighter, he keeps on coming back. He's won everything — Grand Slam, world No. 1, Davis Cup — and he wants more, so you have to respect that."

Ivanovic felt OK after overextending her left knee midway through a point while leading Molik by a set and 3-0. Ivanovic managed to finish off the set 6-0.

"I was a little bit scared because in that one split step that I made I went a little bit low and I felt a sharp pain in my knee," Ivanovic said. "So I thought I better check with the doctors and see what they think. I'm going to go see them afterwards. But it feels fine.

"We had some really tough points and good rallies. I think it was high-class tennis considering it's just the beginning of the year."