It was a McLaren quinella, with Jenson Button ending up second-quickest at the end of the 90-minute session, about half a second adrift of his team-mate.
A dry but cool morning greeted the 24 drivers as the pit lane opened at 10am local time, with the circuit welcoming a selection of significant car upgrades throughout the field.
Red Bull were the early pacesetters in the session, and it seemed to many that the Austrian team might monopolise the timesheets, with an early benchmark in the 1m22s range. However, first Michael Schumacher, then Button, and then Hamilton lowered the times.
Nico Rosberg rounded out the top-six – marking just the fourth time this season he has been out-paced by his multi-championship-winning team-mate. He was followed by Robert Kubica, Fernando Alonso, Vitaly Petrov and Kamui Kobayashi, whose Sauber made a pleasant return to the top-ten in the timesheets.
Paul di Resta – standing in a Force India in place of Adrian Sutil for this session – out-paced Vitantonio Liuzzi to the tune of two places on the timing screens, finishing 13th overall.
Many eyes were on Christian Klien (pictured right), making his first outing for the HRT team as their Friday test driver and his first appearance on in a practice since the 2007 British GP for Honda. He finished up 22nd overall, half a second quicker than Bruno Senna.
Heikki Kovalainen landed up fastest of the rookie team runners, driving the substantially revised Lotus T127 to 18th place on the timesheets. He finished just under two seconds adrift of the next quickest ‘established team’ runner, and one second quicker than his team-mate Jarno Trulli. This was despite the Finn having to get his throttle replaced during the session, courtesy of a sensor failure.
There was little to distinguish those teams who split their revisions between their drivers: Williams and Virgin Racing. Rubens Barrichello put the revised Williams FW32 through its paces, and lapped 16th-quickest despite an oil leak, but he was only 0.1s quicker than team-mate Nico Hülkenberg in the unmodified sister car.
The same applied to Timo Glock, who took a shark-fin equipped VR01 on-track and lapped 0.3s quicker than Lucas di Grassi in the original-spec VR01.
Bottom of the timesheets and without a times lap was Pedro de la Rosa, who was sidelined after three installation laps with a gearbox problem.
2010 Spanish GP Practice 1 Session Times: