US tennis star Coco Gauff revealed she didn’t realise she was about to become world number one in doubles.Gauff rose to the top of the doubles world ranking today after winning the National Bank Open alongside compatriot Jessica Pegula.The pair overcame Nicole Melichar-Martinez and Ellen Perez 6-4, 7-6 in Toronto.It was Gauff and Pegula’s second title at a WTA 1000 tournament this season, having won the Qatar Open in February.Indeed, the 18-year-old Gauff has excelled in doubles over the past 12 months, reaching the finals of the US Open and French Open with Caty McNally and Pegula respectively.She has rocketed up the rankings as a result, but hadn’t realised quite how close to the top she had got.

"Being number one is pretty cool," Gauff said. "I have no words… I didn't really know it was coming this week and what I had to do. But [Pegula] told me yesterday.

"As a kid, I'm going to be honest with you, I didn't even know there was separate rankings for singles and doubles.

“But when I got on tour and when I realised I could do well in doubles, yes… I wanted to. I mean, who wouldn't want to be number one in anything?"

At 18 years and 154 days old, Gauff is the second-youngest player in history to earn the doubles world number one ranking.

She sits behind Martina Hingis, who was 17 years and 251 days old when she rose to the top in 1998.

It is an exciting time for women’s tennis in the US, with both Gauff and Pegula in the top 15 in the singles world ranking.

Pegula also rose to world number eight in the doubles world ranking today.

"I'm so glad that I could help [Gauff] get there today," she said. "I think we're number one in the Race [to the WTA Finals] and the top two Americans in singles.

“So it's been a pretty cool little journey that we're on together, even though I'm ten years older.”

Both Gauff and Pegula are preparing to compete in front of a home crowd at the US Open, which gets underway on August 29th.