Stan Wawrinka has lavished praise on Roger Federer after he reclaimed the world no.1 ranking last week and revealed how he has been impressed by the legendary Swiss' ability to dominate tennis during the twilight of his illustrious career.

Federer became the oldest world no. 1 in tennis history at the Rotterdam Open last week and managed to win his 97th ATP title with a typically elegant victory over world no. 5 Grigor Dimitrov in the Netherlands.

Glory in Rotterdam swiftly followed the retention of his Australian Open crown, a feat that Federer could not imagine achieving during his recovery from a severe knee problem.

The 20-time Grand Slam champion spent over half a year away from the court due to the injury, a period that has made him look forward to retiring from the sport he has mastered for the last 15 years, though he has not devised any plans to call time yet.

Wawrinka, who made Federer's passage to victory in Rotterdam easier when he suffered a shock first-round defeat to Tallon Griekspoor, hitting 41 unforced errors as his poor form from last season showed no signs of abating, has been taken aback by his Swiss counterpart's exploits over the past year and believes the 36-year-old has gone up a level not many thought he could feasibly reach.

"When we saw him win the Australian Open again and take a wild card in Rotterdam, we expected him to get closer to it [world no.1] and to make it happen," Wawrinka said, per Le10 Sport. "It's amazing to see everything he can do and everything he has done in the last 14 months. It has all gone up a notch.

"His whole career has been a record, he has always dominated everything he has done but now, after so many years on the circuit, to have such a level and dominate the current tennis scene as much, it is really impressive."

Roger Federer
Federer was crowned the oldest world number one when the rankings were revised on Monday Getty
Roger Federer