The weather was the best seen so far and the Mercedes driver's morning effort of 1m20.558s, set on Pirelli's soft tyre, proved quicker than anyone could manage in the afternoon. It is also the fastest lap seen at the Spanish circuit in 2013.
For some time nobody got within a second of Hamilton, but Felipe Massa eventually did in the afternoon. The Ferrari driver had several short runs on both soft and supersoft rubber.
His best of 1m21.266s on the supersoft moved him ahead of Adrian Sutil's Force India, just before a wheel came off the F138 and brought out the red flags.
Sutil, who was second fastest in the morning, ran a race simulation in the afternoon, but his earlier 1m21.627s effort was still good enough for third.
Despite delays in the arrival of new Williams parts, and his subsequent late start to the day, Pastor Maldonado ended up fourth.
He handed the FW35 over to F1 rookie Valtteri Bottas for the afternoon. After several runs on harder tyres, he got within 0.2s of his team-mate to finish fifth.
Sauber's Esteban Gutierrez was next thanks to his efforts in the morning. Like Sutil and Toro Rosso's Jean-Eric Vergne, he focused on longer runs in the afternoon.
Mark Webber spent much of the day doing aero work or trying the harder tyres. After the late red flag, he had a quick run on the soft tyre and set 1m22.658s to end the day seventh fastest for Red Bull.
Thanks to Kimi Raikkonen's illness, Romain Grosjean returned to the Lotus for the afternoon and set a best of 1m23.380s for 10th spot.
1. Lewis Hamilton Mercedes 1m20.558s 117
2. Felipe Massa Ferrari 1m21.266s + 0.708s 94
3. Adrian Sutil Force India 1m21.627s + 1.069s 109
4. Pastor Maldonado Williams 1m22.305s + 1.747s 34
5. Valtteri Bottas Williams 1m22.468s + 1.910s 31
6. Esteban Gutierrez Sauber 1m22.553s + 1.995s 99
7. Mark Webber Red Bull 1m22.658s + 2.100s 59
8. Sergio Perez McLaren 1m22.694s + 2.136s 101
9. Jean-Eric Vergne Toro Rosso 1m23.223s + 2.665s 114
10. Romain Grosjean Lotus 1m23.380s + 2.822s 46
11. Davide Valsecchi Lotus 1m23.448s + 2.890s 16
12. Jules Bianchi Marussia 1m24.028s + 3.470s 74
13. Giedo van der Garde Caterham 1m24.235s + 3.677s 126
- Motor Racing
- Sports & Recreation
- Adrian Sutil
- Felipe Massa