World Superbike Championship leader Leon Haslam stamped his mark on proceedings during first qualifying for the second round of the season in Portugal, the Briton coming away with provisional pole position.

Having been edged out by James Toseland during free practice, Haslam, whose win and second place finish at the Phillip Island season opener has given him an early nine point advantage in the standings, stayed firmly in charge during the afternoon session.

With Toseland's best morning effort proving some two seconds off the lap record, it did not take long for some riders to dip below the Yamaha rider's marker when action restarted, with Carlos Checa going first before Cal Crutchlow assumed the lead with a 1min 44.126secs.

It was a benchmark that stood for some time, Crutchlow staying out front for 25 minutes before team-mate Toseland usurped him with a best of 1min 43.735secs.

Holding firm for five minutes, Haslam would go on to creep ahead by one tenth before a following effort of 1min 43.476secs ensured he would not be bettered to the chequered flag.

Michel Fabrizio and Checa did their best to topple Haslam, but both would lose time in the final sector to leave them a threatening second and third.

Having languished outside the top ten for much of the session, Max Biaggi hauled himself up to fourth place late on at the expense of Toseland and Crutchlow, the Yamaha pair nonetheless satisfied with an encouraging opening day performance.

Shane Byrne joined his Althea Ducati team-mate inside the top ten in seventh, ahead of fellow privateer 'twin' counterpart Jakub Smrz on the PATA B&G machine.

Leon Camier and Jonathan Rea followed in ninth and tenth, the British pair edging out Noriyuki Haga, last year's runner-up almost six tenths off the pace in 11th position.

Troy Corser made regular improvements to at one stage be sixth fastest, but would eventually slip down to 12th position on the leading BMW, ahead of Max Neukirchner, who made only a marginal improvement between sessions to drop from third to 13th.

Sylvain Guintoli also found himself well outside the top ten in 14th, ahead of Tom Sykes, who goes into the remainder of the weekend as the sole factory Kawasaki representative following Chris Vermeulen's withdrawal.

Elsewhere, Andrew Pitt gave his Reitwagen BMW team a boost by provisionally out-qualifying factory rider Ruben Xaus, while the team's new recruit, Makoto Tamada, also got to within a tenth of the Spaniard.

With one session remaining before Superpole, the riders currently facing the 'chop' are Sheridan Morais, Matteo Baiocco, Roger Lee Hayden and Vittorio Iannuzzo.