But the Mercedes squad's dominance was temporarily broken as Jenson Button split the German cars. The Briton recorded a lap of 1m26.810s, six-tenths shy of former team-mate Hamilton but almost two-tenths clear of World Championship leader Nico Rosberg.
Vettel's team-mate, Spa winner Daniel Ricciardo, suffered an engine failure that ended his session with around half an hour remaining. The Australian was classified 16th.
A number of non-race drivers made appearances in FP1, including Charles Pic at Lotus, Giedo van deer Garde at Sauber and Dani Juncadella in the Force India. Caterham gave Roberto Merhi his F1 debut as the Spaniard looks to earn the superlicence he will need to make his debut this year.
Italian Grand Prix - Free Practice 1 - Top 10
- Lewis Hamilton (Mercedes)
- Jenson Button (McLaren-Mercedes)
- Nico Rosberg (Mercedes)
- Fernando Alonso (Ferrari)
- Kevin Magnussen (McLaren-Mercedes)
- Sebastian Vettel (Red Bull-Renault)
- Kimi Raikkonen (Ferrari)
- Sergio Perez (Force India-Mercedes)
- Daniil Kvyat (Toro Rosso-Renault)
- Nico Hulkenberg (Force India-Mercedes)