BARCELONA (Reuters) - Nico Rosberg followed up his Spanish Grand Prix victory by stepping back into his Mercedes on Tuesday for another 146 laps of the Circuit de Catalunya in Formula One's first in-season test of the year.

The German was the fastest of the nine drivers on track, with only tailenders Manor Marussia not taking part in the test, with a best time of one minute 24.374 seconds.

His schedule included setup work for next week's Monaco Grand Prix, a home race he has won for the past two years, the evaluation of new parts and some tyre work for Pirelli.

"Today was a great test day for sure," said Rosberg, who is 20 points adrift of team- mate and world champion Lewis Hamilton after five of the season's 19 races and his first victory of the campaign on Sunday.

"The track was a little bit quicker than over the race weekend and we did many laps so I'm a bit tired. But it's my only test during the season so it's important.

"The last sector here has a lot of tight corners - so it's like Monaco in a way, which is useful."