Andy Murray claimed the world number two slot with his ninth career Masters victory in Miami.
Murray now heads into the clay court season brimming with confidence after his 2-6 6-4 7-6 (7-1) win over Spain's David Ferrer.
The British number one lost the first five games in a stuttering start and survived a Hawk-Eye call when match point down in the deciding set.
However, his superior fitness told in stifling conditions, with the victory his first at this level since 2011, although he last year won Olympic gold and his maiden Slam title at the US Open.
"It was such a tough match," said Murray, who was ranked number two for three weeks in 2009, the same year he first won in Miami.
"It could have gone either way, both of us were struggling physically at the end. It's so tough against him.
"He has a great attitude, he's a great fighter. I am sure we will have more tough matches in the future.
"They were incredibly difficult conditions, very windy, extremely humid and hot. I served poorly and if I'd served better, I could have made things easier for myself.
"That's something I'll need to do better during the clay season."
Murray hasn't been second in the world since spending three weeks in the position in 2009.
He will now take a few days off before heading to Monte Carlo in ten days for the start of the clay court season.
However, there was disappointment for Laura Robson, who partnered Murray to Olympic mixed doubles silver last year.
Alongside partner Lisa Raymond, who is 20 years her senior, the 19-year old British number two went down 6-1 7-6 (7-2) in the women's doubles final to Nadia Petrova and Katarina Srebotnik.
© Sportsbeat 2013