In the end, a second five-set match was simply too much for Australian tennis sensation Thanasi Kokkinakis.

The 18-year-old was hailed on the Australian Open’s first night after he went the distance and prevailed over 11th seed Ernests Gulbis.

But against countryman Sam Groth, Kokkinakis wilted in the fifth, losing 3-6 6-3 7-5 3-6 6-1.

The South Australian was far from disgraced, showing his own firepower with 40 winners and 14 aces.

Set the task of backing up the best win of his career just 40 hours after his four-hour marathon was always going to be tough.

Kokkinakis and his team saw the fatigue coming and tried everything to stay the effects.

“I just need to learn how to recover a little bit better because I was feeling pretty sore and flat going into the match,” he said.

“I thought I did all the right things.

“I had like three ice baths; tried acupuncture for the first time to see if that would work.”

Against the big-serving Groth, Kokkinakis had one key take-away from the loss.

“My returning needs to get better,” he said.

“You need a lot of explosiveness against his serve … I felt pretty zapped.

“It felt like a bit of a bluff because inside I was pretty cooked.

Groth has 50 aces in the tournament, and has recorded the fastest serve so far at Melbourne Park of 238km/h.

Kokkinakis, who will play his first-round doubles match on Thursday with Nick Kyrgios, said he would next head to the USA.

“I’ll probably chill out a little bit after this tournament, mentally refresh, then Memphis, Delray (Beach) tournaments.”