LONDON (AFP) - Ivo Karlovic became the oldest man in 39 years to reach the Wimbledon last-16 on Saturday, but his win over Jo-Wilfried Tsonga was clouded by controversy over a double hit.

The 36-year-old Croatian giant fired 41 aces past French 13th seed Tsonga in a 7-6 (7/3), 4-6, 7-6 (7/2), 7-6 (11/9) win and goes on to face either 2013 champion Andy Murray or Italy's Andreas Seppi for a place in the quarter-finals.

But he faced scrutiny after video showed him performing a double hit on a Tsonga set point at 6-7 in the fourth set which would have sent the tie into a deciding set.

The incident was missed by the chair umpire on Court Three but Karlovic insisted the shot was not illegal.

"It was one motion and then if it's one motion it's allowed," said the 2.08m tall Croat who reached the quarter-finals in 2009.

He also said that the television replays were deceptive.

"It's really slowed down," he said.

Karlovic added: "I was going to the net and he hit a cross-court, and I stretched my arm.

"Then the ball hit down on my racquet, and then because it hit down, my racquet went like this, and then it hit here, and then boom, boom. But it was one motion so that is legal.

"I was extremely lucky. I liked it a lot."

Despite the controversy, 2011 semi-finalist Tsonga refused to condemn his opponent.

"I really don't care. What can I do about it now?" said the 30-year-old.

"I just looked at the umpire. He said no. I said OK, next point."

Tsonga added it was up to the officials to apply the rules and that players should not be expected to act as umpires themselves.

"It's the job of the umpire to see it. If he can't see it, I can't do anything. Even if I saw it, I can't say anything."

Karlovic is the oldest man to make the fourth round at the All England Club since compatriot Niki Pilic in 1976.

The 23rd seed is also the oldest to reach the last-16 of any of the four Grand Slams since 39-year-old Jimmy Connors at the 1991 US Open.

"It's a great feeling. I really like what I do. I'm just having fun. So if I'm able to do this at my age, it is unbelievable still," said Karlovic who has rained down 136 aces in three matches.

"And I don't know for how much longer I can do this, but right now I don't have an issue with injuries. And I am healthy, motivated. So I will go on."