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Roger Federer and Nick Kyrgios have played six sets, and all six have gone to a tie-break.

Federer To Face Kyrgios For Return To No. 1

Swiss won their last FedEx ATP Head2Head meeting in Miami

With the No. 1 ATP Ranking on the line, Roger Federer will face one of the best big-match players on the ATP World Tour. The 36-year-old Swiss and Aussie Nick Kyrgios will meet for the third time in their FedEx ATP Head2Head series (1-1) on Saturday in the MercedesCup semi-finals in Stuttgart.

Kyrgios won their first matchup, saving two match points at the 2015 Mutua Madrid Open to beat Federer 6-7(2), 7-6(5), 7-6(12). The big-serving Aussie leaned on his first serve when in trouble and frustrated Federer by winning 83 per cent of those points.

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At the time, Kyrgios was only 20 and just a year removed from stunning then-No. 1 Rafael Nadal at Wimbledon as the 144th-ranked player.

But last year at the Miami Open presented by Itau, Kyrgios was a known threat, and Federer gained revenge in their electric semi-final played under the lights. The Aussie again erased two match points in the second set and belted an ace at 10/9 in the second-set tie-break to even the contest.

Watch The Best Moments From Kyrgios-Federer at 2017 Miami

But the Swiss didn't let another opportunity go by, clinching the semi-final on his racquet 7-6(9), 6-7(9), 7-6(5). He'd complete his third Sunshine Double the next day.

We've had some brutal matches against each other, in Miami, in Madrid,” Federer said after his straight-sets quarter-final win against Argentina's Guido Pella on Friday. “He's always dangerous, especially on the grass. I think I will enjoy playing against him.”

Read More: Relive Kyrgios-Federer From 2017 Miami

Both Federer and Kyrgios have impressed in Stuttgart during their returns to the ATP World Tour. Federer's hiatus was self-imposed; the Swiss skipped the European clay-court swing for a second year in a row after falling in his Miami opener to Kyrgios' countryman Thanasi Kokkinakis on 24 March.

But he's dropped only one set while extending his grass-court win streak, dating back to 2017 Wimbledon, to 14 matches against German Mischa Zverev and Pella.

Kyrgios missed the past two months of singles play because of an injured right elbow, but the 23-year-old Aussie has shown few signs of any lingering problems. He beat German Maximilian Marterer, who made the fourth round at Roland Garros, and 2017 Fever-Tree Championships titlist Feliciano Lopez of Spain to make his second semi-final of the season (Brisbane).

Kyrgios and countryman Lleyton Hewitt are the only two players to beat Federer, Nadal and Novak Djokovic in their first meetings. Kyrgios is also 8-7 against players ranked inside the Top 4 of the ATP Rankings.

If Federer wins, he'll overtake Rafael Nadal for the top ATP Ranking on Monday. The Swiss currently holds the record for most weeks at No. 1 (309). This is Federer's only opportunity during the grass-court season to return to the top spot. He can't improve his points tally at his next two events, the Gerry Weber Open in Halle and Wimbledon, where he won titles last year. Federer was last No. 1 during the week of 14 May.