Valentin Vacherot closed out one of the most stunning big tournament runs in the history of professional tennis by becoming the lowest-ranked player to win a Masters 1000 title as he roared back from a set down to defeat his cousin, Arthur Rinderknech, 4-6, 6-3, 6-3 and triumph at the Shanghai Masters.

There is little precedent for so many of Vacherot’s achievements over the past two weeks. At No 204, the 26-year-old had only narrowly entered the qualifying draw, where he was the second-lowest ranked direct entrant, due to a number of late injury withdrawals. He is the third qualifier to win a Masters 1000 title in the 35-year history of the format and the first Monégasque player to win any ATP title.

“It’s unreal what just happened,” said Vacherot. “I have no idea what is happening. It’s just crazy. I’m just so happy about my performance these past few weeks. I just want to thank everyone who put a brick into my career since the beginning. Sharing this [with Arthur] was really tough, there has to be one loser. But I think there are two winners today, one family that won and I think for the sport of tennis, this story is unreal.”

Vacherot’s performances, which yielded wins over Novak Djokovic and Holger Rune, have been astounding enough but his opponent has made this so much more special. Rinderknech and Vacherot, whose mothers are sisters, grew up together.

It was the 30-year-old Rinderknech, ranked No 54, who convinced Vacherot to compete in the Texas A&M Aggies US college team before turning professional. They have played doubles together on numerous occasions and throughout this tournament they clearly inspired each other to keep on advancing. On Sunday morning, they warmed up on Shanghai’s stadium court with each other.

Arthur Rinderknech (left) and his cousin Valentin Vacherot after the Shanghai Masters final. Photograph: Lintao Zhang/Getty Images

By far the biggest challenge of the tournament for both players was putting their relationship to the side for the day in the biggest occasion of their careers. They had only faced each other once before, with Rinderknech winning in a lowly ITF event in 2018, a result that earned him roughly $400. Here, Vacherot earned $1,124,380 (£823,000), more than double his career earnings.

For a while, as Rinderknech eased through the opening set, it appeared that the more accomplished and experienced player might run away with the match. However, Vacherot gradually worked his way in, finding his feet by building rhythm behind his enormous first serve. When he finally generated a break point, he took it, snatching the decisive break in set two with a searing backhand down-the-line winner and roaring in delight.

By 2-0 in the final set, Vacherot had won five consecutive games and was in full flow. As he desperately dragged himself to the biggest opportunity of his life, Vacherot conceded just three points on his serve in the final set and he closed out his ninth win in two magical weeks with some of his very best tennis.

After Vacherot fired a down-the-line forehand passing shot to seal the win, he shared an emotional hug with Rinderknech at the net. He then scaled his player box and as he hugged Benjamin Balleret, his coach and brother, tears began to fall. Throughout this week, the two cousins have used the customary post-match camera lens signing to encourage each other. This time, Vacherot had only one thought on his mind. “Grandpa and grandma would be proud,” he wrote.

Valentin Vacherot recovered from a set down to win – as he had done three times earlier in the tournament main draw. Photograph: Jade Gao/AFP/Getty Images

The two men sat together as they waited for the trophy ceremony, Rinderknech putting an arm around his cousin, and they both broke down in tears on multiple occasions as they attempted to address and congratulate each other in their speeches. The effort it took for them to break new ground reach this point in their careers was illustrated by Rinderknech rolling off the podium while writhing in pain due to cramps in the middle of Vacherot’s speech.

“Two cousins are stronger than one,” said Rinderknech in French. “You won today, congratulations. I gave it my all. I’m so happy for you, I hope there will be more. I love you so much.”

Meanwhile, Coco Gauff closed out an excellent week at the Wuhan Open by winning her 12th career title with a 6-4, 7-5 win over the sixth seed Jessica Pegula.

Gauff, the WTA No 3, has endured a difficult few months since winning her second grand slam title at the French Open in June, particularly struggling with her second serve. However, she has found her form brilliantly in China, winning the title without dropping a set.

Wuhan marks the 21-year-old’s third WTA 1000 title. She will next head to Riyadh to defend her WTA Finals title.