Lewis Hamilton drew first blood in the battle for the Formula 1 title by outpacing Nico Rosberg in Friday practice for the Abu Dhabi Grand Prix.
Rosberg was faster in the first part of the session when the field was running on the slower soft-compound Pirellis by over six tenths of a second.
But once the field bolted on the super-softs, it was Hamilton who emerged as the pacesetter, shading Rosberg by 0.144s on his first flier and then improving by almost half-a-tenth on his second attempt.
Rosberg subsequently shaved a tenth off his laptime, but ended up 83 thousandths of a second slower than his Mercedes team-mate.
Both had very brief visits to the run-off during the session as they fought for supremacy, but Mercedes still had a crushing advantage on pace.
Kevin Magnussen was best-of-the rest in third place ahead of Sebastian Vettel, but such was the advantage of Mercedes that they were the only other drivers to better Rosberg's earlier top time on the soft rubber.
Valtteri Bottas was fifth fastest, just under a second off the pace, pipping the second Red Bull of Daniel Ricciardo.
Kimi Raikkonen was seventh fastest for Ferrari, but it was a disappointing session overall for the Scuderia as the second car of Fernando Alonso stopped after two laps with a suspected engine problem.
Jenson Button's running was limited thanks to a hydraulic leak that delayed him early on, but he was able to completed 21 laps and ended up eighth fastest.
Scuderia Toro Rosso driver Daniil Kvyat and Felipe Massa rounded out the top 10.
The lead Force India of Sergio Perez missed out on the top 10 by less than two tenths, with Pastor Maldonado 12th fastest.
With Alonso bottom of the timesheets after not setting a time, the returning Caterhams brought up the rear.
But Kamui Kobayashi was just over half-a-second off the back of the midfield pack.
Behind him, Will Stevens completed 33 laps in the second Caterham and continued his learning curve after a disrupted morning session, ending up within five seconds off the pace.