Rafael Nadal described long-time rival Novak Djokovic as "one of the more complex" players he's ever met as they prepare to clash for the 52nd time on Friday with a Wimbledon final spot at stake.
World number one Nadal, the 2008 and 2010 champion at the All England Club, trails Djokovic, the 2011, 2014 and 2015 winner, 26-25 in a rivalry which began at Roland Garros 12 years ago.
Along the way, they have fought out a series of classic and epic battles including Djokovic's 5-7, 6-4, 6-2, 6-7 (5/7), 7-5 Australian Open final victory in 2012.
At five hours and 53 minutes, it was the longest final ever at a Slam.
The following year, Nadal downed the Serb, who was world number one at the time, 6-4, 3-6, 6-1, 6-7, 9-7 in the semi-finals in Paris, this time in four hours and 37 minutes.
"It's always a big challenge to face Novak," said 32-year-old Nadal who is back in the semi-finals at Wimbledon for the first time since 2011 when he finished runner-up to Djokovic.
"He is one of the more complex players that I ever saw in our sport. You know that you can't win against him if you don't play very well."
For his part, Djokovic is eyeing a 13th major after making the semi-finals of a Slam for the first time since finishing runner-up at the 2016 US Open.
Djokovic's 2017 Wimbledon campaign ended in a quarter-final retirement with an elbow injury which led to surgery and precipitated a worrying dip in form and confidence.
Nadal had not dropped a set at the tournament until the quarter-finals where he fought back to defeat Juan Martin del Potro 7-5, 6-7 (7/9), 4-6, 6-4, 6-4 on Wednesday.
Friday's other semi-final pitches Anderson, the eighth seed who lost to Nadal in last year's US Open final, against ninth-seeded American John Isner. Isner beat 2016 runner-up Milos Raonic in the quarterfinal while Anderson stunned eight-time champion Roger Federer. Both men are in the semi-finals at Wimbledon for the first time.