SHANGHAI (AP) Mercedes drivers Nico Rosberg and Lewis Hamilton set the early pace at the Chinese Grand Prix on Friday with the fastest times in a start-and-stop practice session beset by a number of tire problems.
Rosberg had the quickest lap time at 1 minute, 38.037 seconds, just ahead of his teammate, Hamilton, at 1:38.183.
Ferrari's Sebastian Vettel had the third-fastest time of the session, a full half-second behind Hamilton.
Red Bull's Daniel Ricciardo and Ferrari's Kimi Raikkonen rounded out the top five.
It was a frustrating session for Williams driver Felipe Massa and Renault's Kevin Magnussen, both of whom experienced tire issues that prevented them from setting a time.
Massa's left rear tire came off the rim as he was going into Turn 5, causing him to spin across the track and come to a stop on the shoulder. When he returned a short while later, he encountered another problem with the same tire and was forced to stop again.
Magnussen's left rear tire blew out on the back straight toward the end of the session, bringing the red flag out as debris was cleared from the track and halting practice for 20 minutes.
Pirelli posted on Twitter that Massa's tire problems were not caused by a puncture, but rather ''technical trouble.''
There was no immediate word on the cause of Magnussen's problems.
Even Mercedes was not immune from trouble. Hamilton spun twice at the same corner, telling his team over the radio, ''I keep having this locking into Turn 11.'' And Rosberg was forced to end his session early when he encountered a possible engine issue.
Red Bull's Daniil Kvyat had the sixth-fastest time of the morning, followed by Toro Rosso's Carlos Sainz in seventh, McLaren's Jenson Button in eighth, Force India's Nico Hulkenberg in ninth and Toro Rosso's Max Verstappen in 10th.
McLaren driver Fernando Alonso returned to the track for the first time since his spectacular crash at the season-opening Australian Grand Prix last month, setting the 12th-fastest time of the morning at 1:40.538.
Alonso was ruled out of the Bahrain Grand Prix two weeks ago as he continued to recover from a fractured rib. He was cleared to take part in Friday's practice, but FIA doctors were to perform additional tests after the session to determine if he's fit enough to continue through the weekend.
