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With his comeback win over Robin Haase in Rotterdam, Roger Federer is set to become the oldest-ever ATP No. 1 on Monday, at the age of 36. It will be Federer's first time holding the top ranking since 2012.

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Federer first achieved the No. 1 ranking in 2004, 14 long years ago.

Federer will surpass Andre Agassi, who held the previous record of 33. Agassi and his longtime coach Brad Gilbert both chimed in on Twitter to congratulate him.

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The Swiss also received messages from a pair of tennis legends ...

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...as well as a set of twins, one of whom was recently the WTA No. 1.

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Plenty of others chimed in:

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Going forward in Rotterdam, Federer has an unseeded semifinal opponent in Andreas Seppi. In the final, he could see either Grigor Dimitrov or David Goffin. His next event will be Indian Wells.

World erupts for Federer's return to No. 1

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This Week on Tennis Channel Plus 2/12

ATP Buenos Aires (Feb. 14-18)

-Watch Tennis Channel Plus live coverage of Dominic Thiem and Argentina Open beginning Monday February 12 at 12 p.m. ET.

-Can’t make it to Buenos Aires? Watch every match from the Argentina Open on-demand with Tennis Channel Plus.

ATP Rotterdam (Feb. 13-14)

-Don’t miss extended ATP Rotterdam Court 1 coverage live on Tennis Channel Plus Tuesday February 13 at 6 a.m. ET.

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