Red Bull's Mark Webber set a forbidding pace on the first day of the final pre-season test.
The Australian ended a rain-hit day, which concluded with about an hour of dry running, 1.655 seconds clear.
Felipe Massa's day ended early when he stopped on track after Ferrari deliberately ran him out of fuel.
Webber set his fastest time on 'soft' tyres, which are about 0.5secs a lap quicker than the 'medium' tyres Hamilton was using.
Massa had at one point been just 0.054secs off Webber's pace when they were both running at the same time on medium tyres, but the Brazilian slipped down the timesheets as others improved following his breakdown and ended the day eighth fastest.
Massa believed that conditions helped Webber achieve the quick run.
"It was a positive day. The time is not important, but what is important is when I was on the track the car was working well," said the 31-year-old.
"For sure, the lap time was good from Webber at the end, but it was a good time to do it on the completely dry track, and I had stopped. We know his car is good so it is nothing really surprising."
The Red Bull looked very impressive throughout the afternoon, and was more than a second quicker than rivals on the track at the same time at least one other time.
But lap times in testing are notoriously unreliable indicators of form as it is impossible to know the fuel loads the cars are running, which have a big impact on lap times.
Hamilton's impressive performance in the morning included a series of laps when he was two seconds faster than anyone else on the track.
Hamilton ended the morning session 0.234 seconds faster than Massa, with Toro Rosso's Vergne third.
"It was about getting more miles in the car and getting myself back into the race mode, understanding the tyres, how to save fuel," summed up Hamilton. "All those things I already know but just need refreshing.
"There are some things that are better than my old car and some things we can improve. There are some real positives in the car. We are working on reliability issues and the negatives we face."
Hamilton added that Mercedes had some new parts to try later in the test and he expected to run them on Saturday, when he is next in the car. His team-mate Nico Rosberg drives on Friday.
The teams are at Barcelona's Circuit de Catalunya for four days of running ahead of the first race in Australia next month.
The forecast is for heavier rain and high winds on Friday before a dry weekend. The test finishes on Sunday.
All 11 teams are in attendance, alternating their drivers through the test in different ways.
FINAL PRE-SEASON TEST, CIRCUIT DE CATALUNYA, DAY ONE, FASTEST TIMES
1. Mark Webber (Aus) Red Bull-Renault 1:22.693
2. Lewis Hamilton (GB) Mercedes 1:24.348
3. Jean-Eric Vergne (Fra) Toro Rosso-Ferrari 1:25.017
4. Valtteri Bottas (Fin) Williams-Renault 1:26.458
5. Sergio Perez (Mex) McLaren-Mercedes 1:26.538
6. Esteban Gutierrez (Mex) Sauber-Ferrari 1:26.574
7. Paul di Resta (GB) Force India-Mercedes 1:27.107
8. Felipe Massa (BRZ) Ferrari 1:27.541
9. Max Chilton (GB) Marussia-Cosworth 1:28.166
10. Charles Pic (Fra) Caterham-Renault 1:28.644
11. Romain Grosjean (Fra) Lotus-Renault 1:34.928