World number two Novak Djokovic says part of his flying start to the season is down to an improvement in his serve.
Djokovic is unbeaten in 32 matches since the start of the year and has lifted five titles, including the Australian Open and three Masters Series crowns.
He beat world number one Rafael Nadal in all three Masters finals, including last week on the clay in Madrid.
"My serve is back and working, which is really important for me," he said.
"I was struggling in the last year and a half with that element of my game and I was working really hard, so that hard work is paying off now.
"With a good service you can get some free points which is really important at this level."
But he said that he is also basking in the feelgood factor of having won the Davis Cup with Serbia in 2010.
"I know that feelgood moment is also definitely playing an important role in my success, the success I'm having right now and this confidence that I am feeling."
"I'm not thinking about losing a match, but rather I'm trying to think about winning every match and focusing on being professional."
"I have a great team of people around me who are doing their job great and making my life on the court easier."
Having beaten Nadal on clay for the first time, Djokovic was asked what he thought was the biggest challenge for a player, beating Nadal on clay or beating Roger Federer on grass.
"It is hard to say. Probably a year and a half ago both of those challenges were like mission impossible," he said.
"But I guess everybody started to believe they can win against those guys, I did too."
"I think it is all about your mindset on the court and really trying to go out with a positive attitude and really believe in your abilities and believe that you can win."
"With respect to Federer and Nadal - the most two dominant players in the world in the last couple of years - I don't know I guess (beating) Rafa on clay seemed tougher a year and a half ago."