Jelena Jankovic (left) of Serbia argues with Serena Williams (right) of the USA in front of French umpire Kader Nouni during their quarter-final match at the Dubai Tennis Championships yesterday. (EPA)

AFP/Dubai

World number one Serena Williams’ comeback trail endured further feisty moments with Jelena Jankovic, the former world number one from Serbia yesterday before she reached the semi-finals of the Dubai Open.

The two have exchanged testy words on several occasions, the last time in October when Jankovic appeared to question Serena’s sportsmanship at the WTA Championships in Istanbul.

Now, near the end of Serena’s impressive 6-2, 6-2 win, a dispute blew up over the speed at which the rallies were conducted, an issue which has been a contention between them several times.

It happened when Jankovic appeared to slow the pauses between rallies to the speed she thought Serena had been taking, prompting Serena to hold her arms out wide.

This caused Jankovic to walk towards Kadir Nouni, the French umpire, complaining at length, once gesturing towards Serena as she did so.

The match lasted another four points, when there was a further exchange of words between Jankovic and Serena.

Afterwards Jankovic suggested the umpire might have been at fault. “First he tells me I’m serving too fast,” she said. “Then when I took my time. It was like one minute.

“So you never know what to do. Usually if I go over 25 seconds with whoever I play, you know, warning, time violation. Here it’s like you can do pretty much whatever.  

“I have to follow who knows which rules. If it’s 25 seconds, you play 25 seconds. If it goes over, someone’s not ready, you should be ready.

“I follow when she (Serena) serves no matter how fast or slow she plays.”

Serena was placatory. “I told her at the end I didn’t mean anything, and I’m sorry if I played slow.

“She was like, no - it was more that they say she plays too fast and then they say she plays too slow.

She said she couldn’t get right.”

It nevertheless felt like a sequel to more heated exchanges between the two at Charleston in April when Serena claimed she was not ready to receive and made Jankovic restart her service motion, with Jankovic replying “how long do I have to wait?

That dialogue apparently concluded with Williams saying: “Honestly, you got a problem?”

This time she took trouble to take the heat out of the exchanges.

“I just wanted to make sure.  I don’t like to have a beef with anyone.  I was like, look, are we cool?  Because I’m cool with you.  I’m sorry if anything didn’t go right.”

Serena has every reason for focusing on her tennis. It was as impressive as it had been uncertain in the first set of her comeback match against, Ekaterina Makarova, an unseeded Russia, on Tuesday.

It made her a strong favourite to reach her first final in six weeks, as it earned her a meeting with unseeded Alize Cornet of France, who defeated Carla Suarez Navarro of Spain 7-5, 6-3.

Elder sister Venus Williams continued to raise hopes of a return to the top echelons with her third straight sets win in a row to reach a semi-final against Caroline Wozniacki, the former world number one from Denmark.

The seven times former Grand Slam winner overcame Flavia Pennetta, the seed-destroying Italian, by 6-4, 7-5, with a mixed performance which included a slow start and a tense finish but some typically powerful ground stroking during the guts of the match

“I pray and try a million different things all the time. Serena has been extremely supportive and my family have changed their life style for me. It makes me feel better,” she said.