Championship leader Marc Marquez crashed in practice for Sunday's Australian Grand Prix as title rival Jorge Lorenzo finished fastest.
The 20-year-old Spaniard, who is closing in on the world title in his rookie season, came off his bike early in the afternoon session.
He was uninjured and was able to return to the circuit 20 minutes later.
Marquez finished the day second fastest, 0.294 seconds behind Lorenzo, who clocked one minute 28.961secs.
British rider Cal Crutchlow was sixth fastest, while his Tech 3 Yamaha team-mate Bradley Smith recorded the seventh quickest time.
Marquez is bidding to become the first rookie in 35 years to win the premier class title.
He leads the standings by 43 points and can win the championship on Sunday if he wins the race and closest challenger Lorenzo finishes third or lower.
"The day went well, especially in the morning," said Repsol Honda rider Marquez.
"It's a pity about the crash right at the start of the afternoon run but we went back out with the second bike, which had a totally different geometry, and we had no time in which to change things. Thus, we used the initial set-up for the entire session."
Spain's Alvaro Bautista had the third-fastest lap, 0.477secs down on Lorenzo, with Marquez's Spanish team-mate Dani Pedrosa fourth at 0.517secs.
Seven-time MotoGP world champion Valentino Rossi was fifth quickest.
Pedrosa's afternoon practice session was disrupted when an engine mounting bolt, which was not properly locked, came loose, forcing him to stop on the track.
"Today was very positive, the new asphalt felt good and the tyres worked well for us," said Pedrosa. "The only setback was that we were unable to make the most of all the time available, due to a problem with the bike at the end of the afternoon session."
LCR Honda's Stefan Bradl, who fractured an ankle at Sepang last Saturday, was able to take part in opening practice but finished almost four seconds off the pace and was later declared unfit.
1. Jorge Lorenzo (Spa) Yamaha 1:28.961
2. Marc Marquez (Spa) Repsol Honda 0.088
3. Alvaro Bautista (Spa) Honda Gresini 0.664
4. Dani Pedrosa (Spa) Repsol Honda 0.841
5. Valentino Rossi (Ita) Yamaha 0.886
6. Cal Crutchlow (Gbr) Tech 3 Yamaha 0.963
7. Bradley Smith (Gbr) Tech 3 Yamaha 1.194,
8. Nicky Hayden (Usa) Ducati 1.499
9. Randy De Puniet (Fra) ART 2.113
10. Andrea Dovizioso (Ita) Ducati 2.128