Double 2011 race winner Sandro Cortese led both of Friday's wet practice sessions for the Valencia season finale.
The Racing Team Germany Aprilia rider, who starts this weekend with a slim two-point lead over Maverick Vinales in the fight for third in the standings, was just 0.002sec ahead of title contender Johann Zarco this morning.
But Cortese extended his advantage to almost one second in the afternoon, when his nearest rival was young British rookie Harry Stafford! The Ongetta Aprilia rider had been 14th in the dryer morning session, then moved up the order when the weather worsened.
Zarco was a fraction slower in third for Ajo Derbi, with world championship leader Nico Terol tenth and twelfth during the Friday two sessions.
Aspar Aprilia star Terol, who will start the final round with a 20-point lead over Zarco, was 2.146sec behind Cortese this afternoon.
Alberto Moncayo was fourth this afternoon, despite a nasty fall, with Terol's team-mate Hector Faubel another of the many riders to hit the deck. Triple 2011 winner Vinales was tenth for Paris Hilton Aprilia.
Sunday's race will be the last ever for the 125cc class, which is to be replaced by Moto3 (250cc four-strokes) next season The 125cc World Championship is the last remaining class from the inaugural 1949 motorcycle grand prix season.
Friday practice (2):
1. Cortese (Aprilia)
2. Stafford (Aprilia) +0.911s
3. Zarco (Derbi) +0.949s
4. Moncayo (Aprilia) +1.433s
5. Salom (Aprilia) +1.495s
6. Martin (Aprilia) +1.607s
7. Miller (KTM) +1.868s
8. Rossi (Aprilia) +1.880s
9. Faubel (Aprilia) +1.957s
10. Vinales (Aprilia) +1.982s