Barcelona: Lewis Hamilton's greatest enemy is not Mercedes teammate Nico Rosberg or Ferrari's Sebastian Vettel.

It is, he says, himself.

As he seeks to improve on the supreme form that has lifted him 27 points clear in this year's drivers' title contest after four races, the two-time world champion has admitted he fears nobody.

But he does worry about his own failings.

"I know everyone is talking about the psychological stuff, but the only psychological warfare there is, is within myself. Your worst enemy can be yourself. Hence I am my biggest enemy.

"I want to be the best I can be. I know I can do this, and I know I can do that, and if I don't that really bothers me. Otherwise, I'm not fazed. Generally, I don't get fazed by any of that stuff.

"If somebody goes quicker, I figure out how I can be better. I'm not one to think, 'I've got the upper hand, so keep going, keep doing what you're doing'."

Meanwhile, Hamilton has compared himself to Manny Pacquiao - but intends to see his own attacking style lead to victory at the Spanish Grand Prix on Sunday.

The reigning world champion travelled to Las Vegas last weekend to watch the biggest boxing match of a generation as Floyd Mayweather beat Pacquiao in the most expensive fight in the history of the sport.

But it was the defeated Filipino with whom Hamilton drew similarities as he looks to go all out for a fourth win of the season in Barcelona.

"When I was watching the fight, I felt Pacquiao won," Hamilton said. "He was the attacking one. I felt I had more similarities with him, watching his style, I was thinking he's the attacking guy, he's out there, he's hungry. He wants it more than anything.

"The event was interesting. I walked in and obviously there was tons of people there. I was sitting in one of the best seats there, which was amazing. And then the fight wasn't really good at all," he opined.

Hamilton set the pace in Spanish Grand Prix practice on Friday while Mercedes teammate Nico Rosberg fell foul of the stewards with his first reprimand of the season.

While Rosberg set the fastest lap of the day in the morning session, with a lap of one minute 26.828 seconds, Hamilton was comfortably quicker in the afternoon sunshine at the Circuit de Catalunya.

The Briton's time of 1:26.852 compared to Rosberg's 1:27.616, although the German had gear-change problems, as the sport fired up for its first European weekend of the season. Rosberg was summoned by the stewards, including former world champion Alan Jones, after first practice for a pitlane infringement.

Force India's Mexican Sergio Perez was then fined 1,000 euros for speeding in the pit lane during the second practice.

Hamilton, last year's winner in Spain, has won three of four races this season and started all on pole. He leads Rosberg by 27 points. Ferrari's Sebastian Vettel was third and second fastest in the sessions, but still some way off the Mercedes pace, with team mate Kimi Raikkonen fourth in both. (Reuters)