MELBOURNE (AFP) - Defending champion Novak Djokovic said he had been taking tips from serving maestro Goran Ivanisevic after he hammered down a series of aces in his first-up win at the Australian Open.

Djokovic smacked 14 aces and had a first-serve percentage of 65 percent in his grinding 7-6 (7/5), 6-2, 2-6, 6-1 win over Germany's Jan-Lennard Struff in round one.

The Serb credited his work with Croatia's Ivanisevic, who served up more than 10,000 aces in his career and joined the 16-time Grand Slam winner's team last year.

"Throughout my career my serve was maybe a little bit underestimated because of the quality of the returns and the baseline play," he told reporters late on Monday (Jan 20).

"There were times I was struggling with an elbow injury and I had to change the technique of my serve and a lot of things were happening, but in the last year-and-a-half I feel great serving.

"Obviously I pray to have serving days like I had today all of the time. I know it's not possible but I can back up my serving game from the back of the court."

The 32-year-old came through a mid-match lapse against Struff, the world No. 37, and said he was glad to have an early test as he goes for a record-extending eighth Australian Open crown.

"Historically I had a lot of success in the Grand Slams where I had a tough opponent in the first round, because it gets me going from the beginning," he said.

"I have to be alert, I have to be on a high level and I think I was. Of course, you can always play better and I expect myself to be better as the tournament progresses."