MotoGP rookie Marc Marquez is leading returning Yamaha star Valentino Rossi at the head of the timesheets after the opening four hours of 2013 testing, at Sepang in Malaysia.
The track action began at 10am with seven-time MotoGP champion Rossi, winless since his 2010 victory for Yamaha at the same circuit, moving to the top shortly after midday.
There the former Ducati rider remained until Marquez, who joined Alvaro Bautista in attending a private HRC test at Sepang last November, dipped two-tenths under the Italian's best at 1:50pm.
As of 2pm, the halfway point of day one, Marquez's 2m 1.357s time remains fastest by 0.227s from Rossi with early leader Dani Pedrosa 0.301s adrift on the other Repsol Honda.
Yamaha's reigning double champion Jorge Lorenzo sits fourth but just 0.385s from Marquez, as the factory RCV and M1 riders begin to dominate.
Marquez's best lap is comfortably under the official Sepang race lap record of 2m 2.108s by Casey Stoner. However the newly retired Australian - whose place has been taken by Moto2 champion Marquez - set a 1m 59.607s in last year's pre-season tests.
LCR Honda's Stefan Bradl, who led the timesheets prior to Rossi, has been pushed back to fifth (+0.718s) with Bautista sixth (+0.880s) for Gresini and Cal Crutchlow seventh (+0.926s) for Tech 3 Yamaha.
Eighth place Honda test rider Kousuke Akiyoshi is 1.827s from Marquez.
The leading Ducati rider is Nicky Hayden in tenth place, 1.979s from the top. New team-mate Andrea Dovizioso is currently ranked 13th (+2.580s) out of the 27 riders - race and test riders - to record a lap time.
Marquez's fellow manufacturer rookies, Bradley Smith (Monster Yamaha Tech 3) and Andrea Iannone (Pramac Ducati) are twelfth and 17th respectively.
Englishman Smith is 2.3s from Marquez and Italian Iannone 3.7s.