Davide Valsecchi's laptime of 1:26.014s in the final hour of the morning session on the first day of GP2's three-day pre-season test at Jerez proved to be the best anyone could manage all day.
The DAMS driver was over two tenths of a second faster than Fabio Onidi in the Coloni, who put in a lap of 1:26.217s in the morning that put him just ahead of iSport duo Jolyon Palmer and Marcus Ericsson.
Temperatures climbed as the day went on and all the afternoon laps were slower than the top morning times, with Ericsson putting iSport at the top of the timesheets with a lap of 1:26.407s - almost a tenth faster than Esteban Gutierrez but almost four tenths slower than Valsecchi's morning best.
Esteban Gutierrez was second fastest in the afternoon a tenth back from Ericsson with a late run before the chequered flag ended the session. His Lotus GP team mate James Calado (who won the GP2 Final sprint race in Abu Dhabi in November) was third fastest.
All the GP2 teams were trying out the new Pirelli tyres for 2012, and adapting to a new set of aerodynamic rules and regulations for the upcoming season that gives them more flexibility in set-up options - but which also means a lot more work for them in order to arrive at the optimal settings.
"Being back on track is a real pleasure," said Scuderia Coloni's team principal Paolo Coloni. The whole team was looking forward to this test after the winter break and all the development work we did at home."
"I cannot wait to get on track!" agreed Coloni's driver Stefano Coletti. "2012 will be crucial for my career and in the last few months the team and I worked hard to reach the beginning of the season in the best possible shape.
"The six official testing days of Jerez and Barcelona will allow us to refine all the details ahead of the season opener in Malaysia where we will eventually have a more precise understanding of our potential compared to the other teams," he added.
The only significant incident of the day was Tom Dillmann running wide and clipping the barrier, resulting in the morning session to the red flagged while his Ocean Racing Technology car was recovered to the pits.
Dillmann is not yet one of the confirmed GP2 drivers for 2012, but he has been called up by Ocean to drive for them in the three-day Jerez test while Racing Engineering likewise turned to Nathanaël Berthon to cover this week's track time. Similarly new GP2 entrants Venezuela GP Lazarus gave a test seat to Vittorio Ghirelli, who triggered a red flag in the afternoon session when his car stopped out on track early on.
Rapax, who have yet to make any driver announcements for the upcoming season, opted to call in Dani Clos and Daniel De Jong for this week's tests at Jerez.
The session resumes on Wednesday at 9am local time, 8am GMT.Full times from day 1
of the Jerez GP2 pre-season test.