"She really looks mortal now" - Jon Wertheim on Iga Swiatek after her 3R loss in Cincinnati

World No.1 Iga Swiatek was knocked out in the third round of the Western & Southern Open on Thursday after losing to American Madison Keys, 6-3, 6-4.

While analyzing Swiatek's performance on the Tennis Channel, sports journalist Jon Wertheim said Pole "looks mortal now." Swiatek went on a 37-match winning streak earlier in the year, which included titles in Qatar, Indian Wells, Miami, Stuttgart, Rome and Paris.

" She really looks mortal now," Wertheim said. " She'll have 10 days or so and then we'll see what she can do on the hard courts of New York."

Werthiem looked back at the clay season where Swiatek was "absolutely unplayable" and referred to her unbeaten run from earlier in the season as "one of the greatest streaks in modern tennis history."

"Once we moved off the clay in the French Open, where she wasn't just winning matches, I mean there were stints where she was absolutely unplayable. That 37-match streak is one of the greatest streaks in modern tennis history," he said.

"The last time I played her, she beat me pretty badly, so I’m pretty happy to get that one under my belt” - Madison Keys after beating Iga Swiatek in Cincinnati

Iga Swiatek returns a shot to Sloane Stephens during the Western & Southern Open - Day 5

Madison Keys was at her best on Thursday as she condemned Swiatek to her third loss in seven matches since Wimbledon.

Keys was dominant throughout and her powerful groundstrokes from the back of the court were too much for the World No. 1 to handle. The American hit 17 winners to Swiatek’s six and broke the Pole five times in the match.

Swiatek found herself down 5-0 in the second set before winning four games on the trot. However, it wasn't enough to prevent the American from winning in straight sets.

Speaking after the match, Keys said that she was relieved to get over the line after Swiatek beat her "pretty badly" the last time the two players met at Indian Wells.

“I obviously had a couple of games with a couple of match points but I’m just so happy to be able to get the win. The last time I played her, she beat me pretty badly, so I’m pretty happy to get that one under my belt," said Keys.

“I love playing here. The fans are amazing. Thank you everyone for coming out and cheering,” she added.

Iga Swiatek has gone off the boil since her loss to Alize Cornet in the third round at Wimbledon, which ended her 37-match winning streak. She has since lost to Caroline Garcia (Poland Open), Beatriz Haddad Maia (Canadian Open) and Keys on Thursday.

The Pole will now have a chance to switch off for a bit before the start of the US Open at the end of the month, where she will hope to get back to winning ways.