Home star Jorge Lorenzo emerged on top of Friday afternoon's second free practice session for the Catalunya MotoGP round in Barcelona.
The 2012 title leader dipped under the race lap record during a frantic final seven minutes of track action, triggered when many riders made the switch to the softer compound rear tyre.
Lorenzo had also been quickest earlier in the session, but was sitting second to team-mate Ben Spies when the change to softer rubber propelled Andrea Dovizioso (Tech 3) and later Alvaro Bautista (Gresini) to the top.
But Lorenzo also made the switch and was able to regain the initiative by 0.207s over countryman Bautista by the close of the 45 minutes, with Tech 3 Yamaha's Cal Crutchlow another to run the soft option on his way to third (+0.348s).
His team-mate Dovizioso slipped back to fourth (+0.493s), followed by the top Ducati of Hector Barber (+0.540s).
However many of the big names chose not to run the softer option, which seems an unlikely race choice if the current searing temperatures continue.
Spies (+0.703s) is thus probably looking in much better shape than his eventual sixth position suggests (set on his 13th of 22 laps), while Dani Pedrosa was just a fraction slower to be the top Repsol Honda rider in seventh.
The remainder of the top ten was made up of rookie Stefan Bradl (LCR Honda), Nicky Hayden (Ducati) and reigning world champion Casey Stoner (Honda). Stoner had led the morning session for Repsol Honda.
Ducati riders Karel Abraham and Valentino Rossi then completed the twelve manufacturer bikes - all covered by 1.2sec.
Rossi is riding with the new aluminium swing-arm and electronics package used at a recent Mugello test. Team-mate Hayden has the electronics, but is sticking with the carbon fibre swing-arm.
Local star Aleix Espargaro got the better of Power Electronics Aspar team-mate Randy de Puniet to be the leading CRT rider in 13th place, 2.639sec from Lorenzo.
Colin Edwards, making his MotoGP return after missing Le Mans with a broken collarbone, improved one place relative to this morning to be 16th out of the 21 riders on his Forward Racing Suter-BMW.
Friday practice (2):
1. Jorge Lorenzo
2. Alvaro Bautista
3. Cal Crutchlow
4. Andrea Dovizioso
5. Hector Barbera
6. Ben Spies
7. Dani Pedrosa
8. Stefan Bradl
9. Nicky Hayden
10. Casey Stoner
11. Karel Abraham
12. Valentino Rossi
13. Aleix Espargaro
14. Randy De Puniet
15. Michele Pirro
16. Colin Edwards
17. Yonny Hernandez
18. Ivan Silva
19. Mattia Pasini
20. James Ellison
21. Danilo Petrucci