The second set was one-sided, but Raducanu's three wins in California represent her best tournament since winning the 2021 US Open.

"I think that Iga played a very good level and showed why she is number one in the world," Raducanu told BBC Sport.

"She was very ruthless with the way that she played. I think I was able to stay competitive for the beginning of the match but ultimately she ground me down and by the end of it I was just taking way too long to recover from one rally."

The first four games of the match gave Raducanu plenty of encouragement - both players had two break points as the games were shared.

The solitary break of the first set came in the sixth game, allowing Swiatek to take the opener 6-3 as she began striking the ball superbly.

The world number one's defence was as watertight as ever and the winners started to flow.

Raducanu managed to save four break points at 1-1 in the second set, but could not save a fifth and did not win another game after that.

In her fourth match in six days, at her first tournament since January's Australian Open, the Briton's energy levels dropped significantly and the last few games were a procession.

"I can take a positive week," said the 20-year-old, who nearly withdrew from the tournament because of a wrist injury and the after-effects of tonsillitis.

"I think I had a few good wins earlier against some great opponents. I did two good training weeks in London. They paid off to an extent but ultimately two weeks of training isn't going to cut it against the world number one right now.

"I'm looking forward to playing her after I've got more time under my belt.

"Physically I feel like that's going to be one of my biggest assets. I think that I'm going to be one of the best athletes on the tour, and that's going to be a big part of my game.

"I would say there is a very long way to go, but I'm definitely starting the right work now."

Swiatek wants more support for Ukrainian players

Meanwhile, Swiatek has called on the WTA to offer more support to Ukrainian players as their country continues to defend itself against the invasion by Russia.

Ukrainian Lesia Tsurenko withdrew from Indian Wells before her third-round match with Belarusian Aryna Sabalenka on Sunday for personal reasons linked with the war.

Russian and Belarusian players have been allowed to compete on the WTA tour, but not under their national flags.

"There is a lot of tension in the locker room. Obviously it's going to be there, because there is a war," said Poland's Swiatek, who criticised Russian player Anastasia Potapova for wearing a Spartak Moscow football shirt before her defeat by Jessica Pegula on Sunday.

"But maybe it would be a little bit less if WTA put some action at the beginning to kind of explain to everybody what is right and what is not.

"I totally understand why she [Tsurenko] withdrew. I respect the Ukrainian girls so much, because if a bomb landed in my country or if my home was destroyed, I don't know if I could handle that.

"I feel there should be done a little bit more to help Ukrainian players, because I feel like everything we discuss in tennis is more about Belarusian and Russian players and if they should be allowed.

"I don't think that's right, because we should focus more on helping Ukrainian players and providing them everything that they need, because they basically have to take care of like all their families, and there's a lot of baggage on their shoulders."