There used to be a time when Roger Federer and Rafael Nadal had nothing but good things to say about each other. It was the friendliest rivalry you could imagine in the world of professional sports, but the gloves seem to be coming off this year.
Nadal, the fiery Spaniard, landed the first jab, just before the start of the Australian Open, over Federer's refusal to join the calls for a players' "strike" over the demands made by the ATP.
"His position is easy: do not say anything, all positive, I am a 'gentleman', others get burned," said Nadal before launching an emotional tirade against Federer.
The world No 2 later apologised, saying: "What I said, I said, but I was probably wrong telling you because these things must stay in the locker room. I have always had a fantastic relationship with Roger and I still do. We can have different views about how the tour needs to work, that's all. I feel sorry for saying it because I should have said it to him personally."
Federer also reacted calmly, saying: "For me, nothing changes in terms of our relationship. I'm completely cool and relaxed about it. He seemed the same way - or at least I hope so."
The relationship, however, seems to be changing. At Indian Wells, Federer was asked about the time violations and he did not hesitate in naming Nadal as one of the main culprit.
According to ESPN statistics, Djokovic and Nadal averaged more than 30 seconds between points during their epic five hour, 53 minute Australian Open final in January. The rules allow a maximum of 20 seconds between points at grand slams, and 25 seconds at other ATP Tour events.
"I do believe that officials could be a bit more tough on timing," Federer said. "I'm not complaining a lot, but I don't know how you can go through a four-hour match with Rafa and him never getting a time violation."
Nadal's response was typically belligerent: "You cannot expect to play a six-hour match and play rallies of crazy points and rest for 20 seconds. Somebody's ready to do it. I'm not ready to do it."
Given their growing differences, this war of words might continue for some time. And it will add more spice to a rivalry that has entertained fans for many years.