Serena Williams is still the best women's singles player in the world despite her recent loss at Indian Wells according to current world number one Simona Halep.

The American won a remarkable 23rd Grand Slam at the 2017 Australian Open last year when she defeated her sibling Venus in the final in a 6-4, 6-4 win. As a result of her triumph in Melbourne, Williams regained her world number one ranking for the seventh time in her career.

She was set to play in Indian Wells soon after but withdrew due to a knee injury before revealing in April that she was 20 weeks pregnant and would take time away from the sport. 

Serena Willians and Simona Halep Despite being World No. 1, Simona Halep believes Serena Williams is the best in the world. Pictured: Serena Williams (L) of the United States shakes hands with Simona Halep of Romania after defeating her during their Women's Singles Quarterfinals Match on Day Ten of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2016 in the Flushing neighborhood of the Queens borough of New York City. Photo: Alex Goodlett/Getty Images

After giving birth to her daughter Alexis Olympia in September, Williams returned to competitive action for the first time in 14 months at Indian Wells this month as an unranked player and reached the third round before suffering a straight-set defeat at the hands of her sister on Monday.

"I definitely know her [Venus] well, but she definitely played a little bit better than she normally does,'' Serena said after the match. "She served very consistently. She just did everything great.''

"It's different [playing after pregnancy], I haven't played in over a year. It's definitely not less disappointing, I wish it was. But then I wouldn't be who I am. I just have a long way to go and I look forward to the journey."

Halep, who became world number one for the second time in her career in late February, was one player in the tournament who kept a close eye on the match, having always been an admirer of the Williams sisters.

The Romanian also believes Serena should have been the number one seed in the event because she left tennis as the best player in the world.

"I'm the world No. 1 in this moment," Halep said, as per the LA Times. "But I just watched the best player in the world."

Despite being at the top of the rankings, Halep is yet to win a Grand Slam, having recently lost to Caroline Wozniacki in the final of the 2018 Australian Open in January. It is one of the reasons why she likes to watch the duo play as much as possible as it is always a learning experience for the 26-year-old.

Simona Halep Simona Halep has lost all three Grand Slam finals she has reached. Pictured: A dejected Simona Halep of Romania looks on after losing the women's singles final to Caroline Wozniacki of Denmark on day 13 of the 2018 Australian Open at Melbourne Park on January 27, 2018 in Melbourne, Australia. Photo: Scott Barbour/Getty Images

"It's always nice to watch them. I love the way that they are motivated and they are still playing at this age, Serena with the kid," she added. "So it's a great thing what they do for sport, and it's great that tennis has them."

"It was really fun to come out here and watch the game. And also, you know, I have many things to learn from them. That's why I'm trying just to go in to watch every time I can. Also the motivation, the game, the way that they are hitting in important moments, the way they stay there and they are focused for every ball. So everything in general, I have things to learn."

Halep is currently in the quarter-finals at Indian Wells and will face Croatia's Petra Martic while Venus takes on Spaniard Carla Suarez Navarro. Both matches take place on Wednesday.