Miami: Roger Federer's comeback from injury has been so successful that his compatriot Stan Wawrinka believes he can become the oldest world number one in history at the age of 35.
Federer beat Wawrinka in the final of Indian Wells on Sunday for his second win of the year following his triumph in the Australian Open - his 18th Grand Slam title and his first in four-and-a-half years.
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Those wins have propelled the Swiss master to sixth in the world as he makes excellent progress after a six-month layoff caused by a knee injury.
Compatriot Wawrinka believes that not only is Federer back in form, but he is playing in a noticeably different manner that gives him a chance to return to the pinnacle of the rankings.
"He's playing really well, what is different maybe is he is playing closer from the baseline, preferring, using less his slice, he is using more top spin, putting more pressure all the time, returning better that's the difference I seem," Wawrinka said.
"For sure he has a shot for number one, he has just won the first Masters final. For sure he has a big shot," he told reporters.
Andre Agassi holds the record for being the oldest player to hold the men's No.1 ranking, at the age of 33.
"It is going to be interesting to see. Rafa (Nadal) is playing well also and we will see when Novak (Djokovic) and Andy (Murray) are back from injury, it is going to be really interesting for tennis fans," Wawrinka said.
Wawrinka said it wasn't a shock to see Federer, who now has 90 career titles, back to such form, but that he was particularly impressed by his movement.
"From him nothing is a surprise, but for sure to see him moving that well at that age it is something amazing. It is good for me to see that you can be at the top (at that age). It is amazing to see how he is playing after a six-month injury."