Lewis Hamilton beat Ferrari's Fernando Alonso as the Mercedes driver set the pace in practice at the Chinese GP.
Hamilton recovered from a suspension issue that cut short his first session to beat Alonso by 0.141 seconds.
Mercedes driver Nico Rosberg was third, 0.411secs behind Hamilton.
The Red Bulls of Daniel Ricciardo and Sebastian Vettel were next, ahead of Williams' Felipe Massa, Ferrari's Kimi Raikkonen, McLaren's Jenson Button, and the Lotus of Romain Grosjean.
Toro Rosso's Daniil Kvyat was 10th, from Force India's Nico Hulkenberg and Kevin Magnussen's McLaren.
Hamilton's fastest time came despite him complaining about understeer - a lack of front grip - when he finally made it out on to the track about 20 minutes into the second session.
The Englishman also missed about the same amount of time at the end of the first session as Mercedes decided to ensure they had enough time to fix the car.
"It was a difficult day but it's OK," said Hamilton. "We got some laps in P2. We've been working on the tyres - there has been lots of graining, but the pace doesn't look too bad.
"I missed a bit of practice in P1 which put me on the back foot for this weekend. I went into the session not really happy with the balance of the car, so we have some work to do."
Ferrari had a mixed day under the gaze of their new team principal Marco Mattiacci, who created a bit of a stir by wearing sunglasses all day despite the generally overcast weather.
Mattiacci's predecessor Stefano Domenicali resigned after Alonso and Raikkonen finished ninth and 10th in the last race in Bahrain.
Although Friday practice times are an unreliable guide to form, Ferrari did appear to be in better shape in Shanghai.
Alonso was fastest in the first session and split the Mercedes when the teams were doing their qualifying-style low-fuel runs in the middle of the second session.
Raikkonen missed the first session with unspecified car problems and was 0.827secs slower than Alonso in the second.
BBC F1 pit-lane reporter Tom Clarkson said: "This year's Ferrari has always been competitive in fast corners, where good aerodynamics are important, so the car's pace in sectors one and two is perhaps to be expected.
"But what is a surprise is that Ferrari are only 3-4mph slower than the Mercedes at the speed trap on the long straight. They have made some progress on straight-line speed, although they are being cagey on the details."
Ferrari refused to say what Raikkonen's issues were, but BBC Sport has learned he had problems with his power steering system and the electronics controlling the power-unit.
There were also encouraging signs for Lotus, who have had a torrid start to the season caused by under-investment in the second half of last season.
The team, who were competing for podium places and occasionally victories for much of last year, have been battling at the back of the midfield because of a lack of mileage and understanding of the car.
But the car has a revised floor, new front wing and an update on the Renault engine, which like the Ferrari turbo is lagging behind Mercedes on power so far this season, and it appeared to make a substantial difference.
Grosjean's team-mate Pastor Maldonado, though, had a bad day. The Venezuelan had a number of off-track moments in the first session and then crashed on his way into the pits early in the second session.