A "rusty" Novak Djokovic says his straight-sets thumping of China's Zhang Zhizhen was as good as it gets for an opening match of the summer, and he expects to be even better by the time the Australian Open rolls around.
Djokovic crushed Zhang 6-3 6-2 in 72 minutes on Sunday night to give Serbia a 1-0 lead in their United Cup tie against China in Perth.
World No.15 Zheng Qinwen levelled the tie at 1-1 with a 6-4 6-2 win over world No.119 Olga Danilovic in the women's singles.
Djokovic teamed with Danilovic in the deciding mixed doubles, and they triumphed 6-4 1-6 10-6 (match tiebreak) to seal a 2-1 win just minutes before midnight.
The result means if Serbia defeat the Czech Republic on Tuesday, they will secure a quarter-final berth.
Zhang put up a fight early in Sunday night's singles match at RAC Arena, with his strong serving keeping Djokovic at bay for a while.
But the wheels fell off in the second set for the world No.58 as Djokovic unleashed his full force.
Djokovic's swift movement around the court and powerful groundstrokes wore Zhang down, with the 24-time grand slam winner racing to a 4-0 lead in the second set on the way to victory.
"I was a little bit rusty at the beginning. I was out of the tempo, rhythm for maybe the first five, six games," Djokovic said.
"But that's normal when you don't play an official match for over a month. It takes a little bit of time to get the engines going.
"He was serving well, he had nothing much to lose.
"When I broke his serve at 3-2 in the first set, I felt the momentum shift to my side."
Djokovic, who is aiming to win his 11th Australian Open this summer, is satisfied with how his fitness is tracking.
"I'm still in the process of building the body and the form for Melbourne," Djokovic said.
"The Australian Open is where I want to be at my 100 per cent.
"But this is as good as it gets for the opening week, and hopefully I can build from here and go in the right direction."
Meanwhile, Australia's quarter-finals hopes hinge on a must-win meeting with reigning champions the USA after the Americans' 2-1 victory over Great Britain.
The British took an early lead in Sunday's tie against the US when Katie Boulter upset world No.5 Jessica Pegula 5-7 6-4 6-4.
World No.10 Taylor Fritz, who will face Alex de Minaur on Monday night, squared the ledger for the Americans with a 7-6 (7-5) 6-4 win over Cameron Norrie.
Fritz and Pegula claimed the mixed doubles with a 1-6 7-6 10-7 (match tiebreak) victory over Boulter and Neal Skupski.
Australia, beaten 2-1 by Britain on the tournament's opening night, must defeat the US 3-0 on Monday night to be guaranteed a quarter-final berth. A 2-1 win would mean the qualifiers are decided by sets won in matches between the three teams. A loss and Australia will be out.
Fritz had to take a medical time out in his singles match after struggling with a quad injury sustained through extra sprint training.
"I don't really sprint that often but I carried that into today," Fritz said.
"I felt really sore and I overdid it running for a drop shot but I got through."
Elsewhere on Sunday, former US Open finalist Leylah Fernandez showed her class by powering Canada to a 2-1 victory over Chile.
The world No.35 made light work of Daniela Seguel in the women's singles with a 6-2 6-3 win at Sydney's Ken Rosewall Arena, before teaming up with Steven Diez to win the mixed doubles.
