Rafael Nadal knows how tough it is to work out Dustin Brown but playing alongside the German is just as unpredictable, according to his former doubles partner Jonathan Marray.
Marray began playing with Brown at the French Open in 2012 and the pair enjoyed a successful partnership, reaching four Challenger finals and winning two in Bosnia and Italy.
Brown has since turned his attention back to singles and the 30-year-old inflicted the biggest shock at Wimbledon so far on Thursday night when he dumped out two-time champion Nadal in the second round.
The stunning victory marks a remarkable rise from the days when Brown used to travel to tournaments in a camper-van and strung other players' racquets to save money.
A full head of dreadlocks, which he has not cut since he was 19, and an explosive style of play have both caught the public's imagination and Marray admits even when they played together, he never knew what was coming next.
"I don't think he even knows what he's doing himself half the time," Marray said.
"I didn't really know what he was doing when I played with him. It was like playing against him, you never knew what was coming.
"He played ridiculous shots out of nowhere, angled winners off anything, it was good fun to play with but not such good fun to play against.
"He's totally unpredictable. With most people you have an idea of what they like to do and where their strengths are, but with Dustin it's hard to predict what's coming. It's hard to formulate a plan against him.
"The number of times I played with him and he turned a match in a few points with ridiculous shots. He was great fun to play with and he's a good guy."
Brown moved from Germany to Jamaica when he was 11 years old but later returned to Europe in order to further his career.
His parents bought him a Volkswagen van to help him travel to tournaments, and from 2004 to 2007 Brown chugged around the globe, struggling to afford entry fees, petrol and food.
In 2010 he switched to German nationality and he broke into the top 100 in the same year, before reaching a career-high ranking of 78 in 2014.
"I didn't play that much with him during his camper-van stint but when I played with him he talked about that," Marray said.
"He's a very sociable guy, he knows everyone, and although he's not loud he's always got something to say.
"I did socialise a lot with him off the court. I've known him for years, I played a few future events in Jamaica.
"He was living there and he was just the same as he is now, with the big dreadlocks, and he played the same way.
"He's found a way that works for him and he's a tricky customer that's for sure."
Brown has never been past the third round of a grand slam before but he plays Serbian Viktor Troicki on Saturday for a place in the last 16.
If he wins, Britain's Andy Murray may await in the quarter-finals and Marray believes Brown could cause problems for the British number one.
"He's got that game, especially on this surface, to really mess with people," Marray said.
"He doesn't give anyone any rhythm. Rafa wasn't on his best form but Dustin didn't give him any baseline rallies to get into it. Rafa was totally out of his comfort zone.
"I'm still surprised he beat him but Dustin has the potential for those kind of upsets on this surface."