DIFFICULT DAY
Ferrari arrived in China as favourites after looking dominant in Bahrain, a race they would have won but for a late engine problem that hit Charles Leclerc's car while leading, and with plenty of straight line speed.
Vettel led the opening session, and was hot on Bottas’ heels in the afternoon, while Leclerc had a difficult day.
Both the 21-year-old Monegasque and Vettel are running a new electronic control package as a precaution against a repeat of Leclerc's engine problem.
The youngster's session ended early as he parked up in the garage with some 20 minutes to go so that Ferrari could carry out cooling checks.
"We had to stop for further checks on something on the oil," said Leclerc. "We will check it but no big issues.
"I think it will be very close, Mercedes and also Red Bull are actually quite close, so it will be an interesting battle."
Hamilton was second fastest in the morning but struggled in the afternoon.
"We’re going to work hard tonight to find some tweaks and hopefully come back stronger tomorrow,” said the five-times champion. "The car has the pace in it to compete at the front, we just need to find the right set-up."
Nico Hulkenberg was fifth fastest for Renault, ahead of Carlos Sainz in the McLaren.
McLaren rookie Lando Norris, fresh from having scored his first Formula One points in Bahrain, was eighth for McLaren ahead of Renault’s Ricciardo.
Red Bull’s Pierre Gasly rounded out the top 10.
Friday’s two sessions were relatively trouble free apart from a few spins as the drivers explored the limits and got to grips with the track.
Hamilton and Bottas both spun during the second 90 minutes while Canadian Lance Stroll lost control of his Racing Point at the exit of the final corner in the morning.
The brakes on Alex Albon’s Toro Rosso also caught fire at the end of the session with Ferrari mechanics standing close by and helping to douse it.
