The duo, who snapped photographs of the action on court, kept their style cool and casual. Niall opted for a white shirt while Liam wore a long-sleeved sweater.
One Direction are currently in the middle of the European stint of their Where We Are tour, which has already taken in South America and the UK, including Croke Park and three nights at Wembley Stadium.
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Liam and Niall, as well as their bandmates Harry Styles, Louis Tomlinson and Zayn Malik, played in Amsterdam on Wednesday, and now have two days off before they fly to Milan on Saturday for two concerts in the Italian city.
The tour kicked off at the end of April to promote their third album, Midnight Memories, but the five boys have found the time to focus on other pursuits as well.
Last week it was confirmed that Louis had purchased Doncaster Rovers Football Club, teaming up with the club's former chairman John Ryan.
Liam Payne and Niall Horan at Wimbledon 2014
Louis, who is estimated to be worth £15million, followed up a Twitter post announcing his news with another tweet asking fans to donate to the Tomlinson Ryan Trust.
"Ahhhh here we go :) We want you to be part of our big idea for #drfc on @CrowdfunderUK: http://www.crowdfunder.co.uk/trust #FansUnited," he posted.
The crowd funding campaign is aiming to raise £2million for the football club and the target amount will most likely be reached in no time. In the first ten minutes, the donation page received £500,000.
Harry, meanwhile, recently gave one bride a real dilemma on her wedding day, recording a special video pleading with her to jilt her husband-to-be.
Looking down from the camera, the cheeky heart-throb says: "Tash, you don't have to go through with this. It's not too late."
Struggling not to smile, he continues: "I'll be at Orli's in Borehamwood for the next three hours. If you don't come I'll understand… but that's where I'll be."