Frentzen tops warm-up as surprises continue.

Heinz-Harald Frentzen came out on top of the pre-race warm-up in Monaco, adding another unexpected twist to Jarno Trulli's practice pace and Juan Montoya's pole position.

The German did not move to the head of the times until the final ten minutes of the half-hour session, having had to play second fiddle to a host of Michelin runners, but bounced back as the chequered flag unfurled to snatch the honours back from fellow countryman Michael Schumacher.

The world champion had also been quiet early on, but dropped the target below 1min 21secs with two minutes remaining. Until then, the session had been fought over by the two Williams and McLaren drivers. David Coulthard and Kimi Raikkonen finished third and fifth respectively, but there were problems for pole sitter Montoya, who managed just 20th position after calling for wing changes on his FW24.

The Colombian was the first to show at the head of the times, gradually whittling away at his initial mark of 1min 36.8secs, but stopped to have adjustments made to both his race and spare cars, losing time to regain his place at the front of the field as the session wore on. Instead, it was team-mate Ralf Schumacher who took over as the times dropped into the 1min 24s.

Michelin continued to show well, despite the cooler temperatures produced in the early morning session. McLaren, boosted by Coulthard's front row start pushed both its cars into top spot, with the Scot's young team-mate Raikkonen enjoying his first trouble-free session of the weekend to battle with the #3 car mid-session.

Coulthard continued to scrap with Frentzen when the Arrows driver made his appearance among the pace-setters, but eventually had to give second best to the German, as well as the Ferrari of Michael Schumacher.

Fourth place went to Trulli, who continued to show Renault's potential and that of Michelin. Sadly for the Italian, seventh on the grid means that he is relying on problems for the frontrunners - and not being caught up in trouble himself - if he is to break his duck for the season. Team-mate Jenson Button was eleventh overall.

Rubens Barrichello backed up his Ferrari team leader in sixth, one place ahead of Ralf Schumacher's Williams, which used the session to help scrub tyres for the race. Olivier Panis was eighth, giving BAR some encouragement after a difficult practice, while Giancarlo Fisichella underlined his Monaco expertise with ninth for Jordan. Mika Salo was tenth.

As ever, though, the true accuracy of the session was masked by doubts over the exact strategy and set-up of the various cars, with those at the back of the grid perhaps trying lighter fuel loads, and those at the front planning to run longer and heavier at the start with overtaking at a premium.

Allan McNish showed that Toyota will be a force in race trim by taking twelfth spot, one ahead of the impressive Mark Webber. The Australian may be one of those planning to run light in an attempt to make up places early on, and finished ahead of the man who ran the same ploy in Austria, Jacques Villeneuve.

Sauber continued to struggle, trailing the second Arrows of Enrique Bernoldi in 15th and 16th, while Takuma Sato took 19th for Jordan. There was no joy for Jaguar, either, as Pedro de la Rosa and Eddie Irvine clocked only the 18th and 21st best times, with the Spaniard spinning at the chicane, the only misdemeanour of the session.