World number two Novak Djokovic believes it is harder to win a Masters series title than a Grand Slam.
Speaking after he breezed into the third round at the Rome Masters, the Serbian 23-year-old explained why a one-week tournament is more physically demanding than one that lasts twice as long.
In Grand Slams, a player who reaches the final will have to play seven best-of-five set matches over 14 days. To earn success in a Masters event, he must play five best-of-three set matches in just seven days.
"Grand Slams are very special tournaments, they're different to all the others," said Djokovic.
"You play over two weeks and you have to win three sets (in each match), you have to stay concentrated and maintain the desire to win always.
"But here, may be it's physically tougher to play every day. It's not important whether you're playing two or three sets but the fact that every day you're playing someone in the top 10 or 15 or 20 in the world."
"Over three weeks (three successive tournaments) that takes a lot out of you but that's tennis."
Djokovic won in Madrid last week and in Belgrade the week before and he continued that imperious form against an erratic opponent, beating Poland's Lukasz Kubot 6-0, 6-3 in just over an hour.
Kubot, ranked 141 in the world, came through qualifying to reach this stage of the competition and the gulf in class between the pair was evident from the off.
Djokovic raced through the first set taking all three of his break-point opportunities, making half the number of errors and four times as many winners.
On the final point he pounced on a net-cord to send a forehand winner down the line.
Serve and volley specialist Kubot seemed to gather his strength and put up much more of a fight in the second set.
A winning smash in the fourth game gave him game point which he took with a delicate drop shot that brought up the biggest cheer of the match and an appreciative smile from the outclassed Kubot.
He was again on the attack in his next service game, and he secured that at the third attempt with a forehand volley winner.
Kubot held serve once more but Djokovic finished off the match when the Pole blazed a forehand into the tramlines after just one hour seven minutes on court.
Djokovic will play Stanislas Wawrinka next after the Swiss 14th seed beat Italian wild card Filippo Volandri 6-1, 3-6, 6-2.
Having come from high altitude in Madrid and what many believe to be the fastest clay courts in the world, Djokovic said that the conditions in Rome had not been that different.
"It's quite different but still it's quite fast here, it's more similar to Madrid so it didn't take me a while to get used to the conditions," he said.
"(Kubot) was making a lot of unforced errors and coming to the net so he didn't give me a lot of rhythm but I'm confident I can play well in these conditions."
Having spent three weeks in a row at a tournament, Djokovic admitted that he is missing out on some physical preparation.
"I like to practise, I like to work on things and always improve and what I've lacked in the last couple of weeks is some physical workouts because this is my third week in a row and I don't have much time," he said.
"I'm basically playing a match every day. But I'm maintaining my good feeling on court and good physical condition off court and trying to keep it up because I know Roland Garros is coming, which is the most important tournament for me on clay."