Rubens Barrichello set the pace in the first practice session for the Monaco Grand Prix as the Brawn GP driver aimed to put behind him the disappointment of Barcelona.
Barrichello, who set his best time two thirds of the way through the session, outpaced Ferrari's Felipe Massa by 0.310s, while world champion Lewis Hamilton was third fastest.
With an emphasis on track time and the need for drivers to dial themselves in as well as their cars, there was for once only a brief wait between the usual installation laps and running proper on Thursday morning.
First out, naturally, was Toro Rosso's rookie Sebastien Buemi, whose long sequence of laps saw him occupy the top spot almost until the 30-minute mark, at which point he was eclipsed by Toyota's Timo Glock.
The German's 1m20.548s was never likely to last however, as the circuit's grip improved with more rubber continuously being laid down, and very quickly Ferrari's Massa moved ahead.
Glock didn't go down without a fight though and the pair began an fascinating battle at the top, each replacing the other at the top for several laps running. That was until Massa and team-mate Kimi Raikkonen firmly established themselves at the top.
It stayed that way until halfway through the session when 2008 winner Hamilton, always inspired at Monaco, moved to the top with a spectacularly and characteristically lairy lap - 1m18.376s
As if to prove that was no fluke, the Briton then improved on that with an excellent 1m17.578s effort.
Hamilton led the way from Massa, Williams's Nico Rosberg and Red Bull's Mark Webber until Rubens Barrichello thumped in a smooth lap that moved him to the top for Brawn with 25 minutes to go. The Brazilian then improved again to 1m17.189s.
The frantic action, oddly, then suddenly stopped, following an engine failure suffered by Sebastian Vettel which set up a dramatic final ten minutes as several drivers broke the lull by rejoining the track on super-soft Bridgestones.
Ironically though, the fact that nearly the entire field came on track all at once, meant that they all tripped over one another, despite the best efforts of Hamilton, Button and Rosberg, allowing Barrichello to remain on top.
Behind the top three was Heikki Kovalainen, who set his laps in the dying seconds of the session, ahead of Raikkonen and Williams driver Kazuki Nakajima.
Rosberg ended up seventh after his final lap was apparently thwarted by Hamilton, while Button, Fernando Alonso and Mark Webber completed the top ten.
Other than Vettel's engine failure, other incidents included Hamilton, Kovalainen and Button all running wide at St Devote. And, according to reports, a fire extinguisher going off in the pitlane.
Pos Driver Team Time Laps
1. Barrichello Brawn-Mercedes (B) 1:17.189 25
2. Massa Ferrari (B) 1:17.499 + 0.310 31
3. Hamilton McLaren-Mercedes (B) 1:17.578 + 0.389 25
4. Kovalainen McLaren-Mercedes (B) 1:17.686 + 0.497 29
5. Raikkonen Ferrari (B) 1:17.839 + 0.650 30
6. Nakajima Williams-Toyota (B) 1:18.000 + 0.811 29
7. Rosberg Williams-Toyota (B) 1:18.024 + 0.835 27
8. Button Brawn-Mercedes (B) 1:18.080 + 0.891 27
9. Alonso Renault (B) 1:18.283 + 1.094 30
10. Webber Red Bull-Renault (B) 1:18.348 + 1.159 22
11. Buemi Toro Rosso-Ferrari (B) 1:18.695 + 1.506 36
12. Piquet Renault (B) 1:19.204 + 2.015 36
13. Vettel Red Bull-Renault (B) 1:19.233 + 2.044 16
14. Bourdais Toro Rosso-Ferrari (B) 1:19.255 + 2.066 30
15. Fisichella Force India-Mercedes (B) 1:19.534 + 2.345 27
16. Kubica BMW-Sauber (B) 1:19.560 + 2.371 20
17. Heidfeld BMW-Sauber (B) 1:19.579 + 2.390 22
18. Sutil Force India-Mercedes (B) 1:19.600 + 2.411 23
19. Glock Toyota (B) 1:19.698 + 2.509 23
20. Trulli Toyota (B) 1:19.831 + 2.642 28
All Timing Unofficial