The start of the match was delayed and then later interrupted by rain when Gauff was leading 1-0 in the second set. She maintained her momentum when play resumed to claim a dominant win over her Tunisian Group B opponent.

"I got a marriage proposal yesterday so I'm feeling the love here in Cancun," Gauff said with a laugh after the match, thanking the crowd who showed up despite the weather.

"I honestly wasn't expecting as much support today...I appreciate you guys and hopefully we can get a lot more people to come as the week continues."

The American's first victory in WTA finals came after a winless campaign last year and it made her the first American teenager to win a match at the WTA Finals since Venus Williams in 1999.

In September, Gauff became the first teenager to win the US Open since Serena Williams in 1999.

"Zendaya sent me flowers to my house," Gauff told Tennis Channel after Monday's win, referring to the actress as she spoke about life after winning the grand slam.

"It was like a huge bouquet of flowers. My brother and I struggled to lift it up on the table. I think it weighed at least 50 pounds. It was so heavy. I think that was the coolest thing."

Gauff revealed that her focus through the match was to not let the rain interruption derail her.

"Sometimes you win a couple games and the rain delay happens and the match can completely turn around," she said. "But I was able to stay steady the whole time."

Gauff, who qualified for the WTA Finals as the third seed, will face second seed Iga Swiatek in her next Group B outing on Wednesday. Swiatek started her campaign earlier on Monday with a 7-6(7-3), 6-0 win over Marketa Vondrousova.

Swiatek, a Polish former world number one, beat Gauff by straight sets in last year's WTA Finals, and won three of their four subsequent matches.