Roger Federer added another achievement to his amazing career last night, returning to the No.1 spot at the top of the ATP rankings.

After his victory on Friday, he became the oldest player ever to reach the top, eclipsing Andre Agassi who was 33 at the time. As well all know, Federer is 36.

Beating Robin Haase 4-6, 6-1, 6-1 in the quarter-finals in Rotterdam means Federer becomes the oldest player - either male or female - to top the rankings, surpassing Agassi, who held the record at the age of 33.

On the way to this unique record, Federer once again demonstrated some of his famous sportsmanship.

The Swiss had just won the second set 6-1 to level the match, as Haase managed to win the first set.

Leading 1-0, 40-15 in the third, Federer served wide to Haase's forehand, appearing to have hit a direct ace.

The crowd cheered, but Federer began to line up for his second serve, having no doubt that the ball was out.

Haase stood in bemusement, as if he trusted Federer more than the judges.

The Dutchman waved to Roger and called out across the court: "Roger, no one called 'out'."

The Swiss' reply was simple -  "It's out".

The referee had no choice but to trust the legend, letting him proceed to his second serve.

Have a look at the funny situation below.

It was announced by the commentators later that Hawk-Eye system showed the ball out by 3mm!

Federer went on and won the point anyway due to an error from Haase's forehand, extending his lead to 2-0 and bringing himself four games away from the semi-finals.

"The Maestro" gave only one more game away to his opponent, winning the set 6-1, securing the match and the record world number one spot in the process.

The next obstacle between Federer and the title in Rotterdam is Andreas Seppi, who overcame Daniil Medvedev in his last match. The other place in the final will be decided between David Goffin (Bel) and Grigor Dimitrov (Bul).