(CNN)Like fans have seen so many times, Tiger Woods was up on his feet and pumping his fist in celebration.
Tiger Woods enjoyed watching Rafael Nadal's win against Marin Cilic at the US Open
But the 15-time major champion's jubilation wasn't over a shot that he had made on the golf course. It was to cheer on his friend, Rafael Nadal.
Nadal went on to defeat No. 22 seed Marin Cilic of Croatia 6-3, 3-6, 6-1, 6-2 on Monday to advance to the US Open quarterfinals. The 33-year-old Spaniard and world No. 2 dazzled with spectacular shot-making -- including a mindbending shot around the net on the second-to-last point of the match.
"Just an incredible performance and awesome way to close out the match," Woods said in a tweet.
In his on-court interview, Nadal was asked about Woods.
"For me, it's a huge honor playing in front of all of you of course," Nadal said to the crowd. "But playing in front of Tiger for me is a very special thing.
"I always said I never had big idols, but if I had to say one, one idol is him. I always tried to follow him every single shot that he hit during the whole year.
"For me, it's a big pleasure to have him here supporting. Means a lot. He's a big legend of the sport, one of the greatest sportsmen of all time. I just want to congratulate him for one of the more amazing comebacks in sport, winning the Masters this year."
Nadal, who likes to golf as a hobby, was asked if Woods has given him any advice on his golf game or if they have ever played together.
"Honestly, it's much better if Tiger doesn't see my swing," Nadal said, drawing laughs from Woods and the rest of the crowd. "Maybe he can lose a little bit of rhythm after that."
Nadal, seeking his 19th major title, will face No. 20 seed Diego Schwartzman of Argentina in the quarterfinals.