Serena Williams is back to her best and looks a sure favourite to win the US Open title. Photo: Robert Deutsch/USA TODAY Sports

After one of those Williams sisters showdowns that rarely fail to disappoint, we are back to the old debate at a Grand Slam event about who might be able to stop Serena.

Following a crushing 6-1, 6-2 defeat both of them claimed that it was among the younger sibling’s best performances in their 30 meetings.

Yesterday was the first birthday of Serena’s daughter, Olympia, and a year on from becoming a parent her movement on the court is starting to look back to its old efficiency.

Not that there were any celebrations — the cause of some awkward moments during interviews last week amid all the gushing over her — as the American great is forbidden from indulging in such things as a Jehovah’s Witness.

Instead, Williams. 36, was preparing for her fourth round against Estonia’s veteran Kaia Kanepi, who upset top seed Simona Halep in the first round.

Venus’s verdict on the match sounded ominous for other players left in the last 16. She said: ‘I think it’s the best match she’s ever played against me. I don’t think I did a lot wrong. But she just did everything right.

‘Obviously that level is definitely where she’s going to want to stay during this whole tournament. She didn’t win that match because I just rolled over. She played untouchable tennis.’ But the older sister, 38, somewhat undermined her remarks by also coming out with some of her thoughtless nonsense. ‘She’s been in incredible form coming into the tournament,’ said Venus.

In fact, Serena had played three matches since making the Wimbledon final in July. She lost two of them, one being a hiding from British No 1 Jo Konta.

‘I think it’s by far the best match I ever played against her in forever but I don’t know about ever, ever,’ said Serena. ‘I played much better than I have since I started this journey on my way back.’

The latter statement definitely looks accurate after an encounter which was never going to live up to all the hype and which took place amid a leaden atmosphere compared to the exhilaration of the Rafael Nadal-Karen Khachanov match that preceded it.

If anyone is likely to beat her then it will probably be a skilled counter-puncher equipped with strong defence. The biggest threat remaining in her half of the field looks like the mercurial defending champion Sloane Stephens, who she could face in the semi-finals. Last night, another potential foe, the Wimbledon champion Angelique Kerber, was facing Dominika Cibulkova in her attempt to join Williams in the fourth round.

In the men’s event, Andy Murray’s conqueror Fernando Verdasco was defeated 7-5, 7-6, 6-3 by Juan Martin Del Potro, the 2009 champion who is due another strong run here.

On Tuesday, Murray is likely to be named in the five-man squad for Great Britain’s Davis Cup tie against Uzbekistan in Glasgow, beginning a week on Friday, and the last match played in the UK under the outgoing format of three days and best-of-five sets.

There are expected to be caveats about his playing time dependent on how his body has held up after the exertions of this week.

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