SEPANG  - Spain's Dani Pedrosa stormed to victory in the shortened Malaysian Motorcycle Grand Prix Sunday, keeping his championship title chase alive on a rain-soaked circuit with his sixth win of the year.

The Honda rider passed pole-sitter and Yamaha ace Jorge Lorenzo, who is the championship points leader, midway through a race which saw a raft of riders crashing out. Organisers put out the red flag on lap 13 of the 20-lap race to stop the event due to the torrential rain.

It is Pedrosa's third successive race win since moving up to the MotoGP class. He won the race in 29 minutes 29.049 seconds while Lorenzo was 3.774 seconds behind. Pedrosa's Australian team-mate Casey Stoner, recovering from an ankle injury, was third after starting from the second row. Stoner clocked in at 29 minutes 36.193 seconds.

With his first ever win in wet conditions, and battling for his first MotoGP crown, Pedrosa -- who started second on the grid -- narrowed the points gap with his countryman Lorenzo, on 321, to just 22.

There are two more races left in the 2012 season, in Australia and Valencia. Lorenzo charged away from the pack at the start with hopes of winning for the first time in the MotoGP class at Sepang. But as increasingly heavy rain began to hit the circuit, Pedrosa brilliantly picked up speed and caught his arch-rival.

"It is my first winning in the wet and I am very happy. I could get some rhythm and maintained a constant lap," he said. Lorenzo said the red flag came out just as Pedrosa overtook him.

"I was struggling when heavy rain poured on the track. I am lucky to be second. It (the 20 points obtained for second place) is good for the championship title," he said. Lorenzo has finished second on the last six occasions he has started from pole position. The only race he won from pole in 2012 was the season opener in Qatar. Stoner, who has 230 points, missed three races this season after injuring his right ankle in qualifying at the Indianapolis Grand Prix. He returned last weekend at Motegi and plans to retire at the end of this season.

Nine-time world champion Valentino Rossi who has had a bad season for Ducati, finished fifth behind his American team-mate Nicky Hayden. Alex De Angelis won the Moto2 race at a rain-soaked circuit, with Australian Anthony West coming second in an action-packed event. British rider Gino Rea, a successful supermoto rider, was third on a Suter. Pouring rain cut the 19-lap event to 15 laps after an earlier heavy shower delayed the start of the race. German KTM rider Sandro Cortese won the Malaysian Motorcycle Grand Prix to be crowned the inaugural Moto3 world champion.

The 22-year-old also became the first German rider to win the lightweight class world title since Dirk Raudies in 1993 and the first ever rider to take a road-racing world title for KTM. Cortese will migrate to the Moto2 class for the 2013 season.

Meanwhile, Alex De Angelis won the Moto2 race at a rain-soaked Sepang circuit Sunday, with Australian Anthony West coming second in an action-packed Malaysian Motorcycle Grand Prix. British rider Gino Rea, a successful supermoto rider, was third on a Suter. San Marino's De Angelis, riding a FTR machine, clocked 36 minutes 57.793 seconds. West on a Speed Up was 0.710 seconds behind De Angelis while Rea was 1.363 seconds behind the winner.

Pouring rain cut the 19-lap event to 15 laps after an earlier heavy shower delayed the start of the race. The race on the 5.5 kilometre (3.4 mile) track exploded into action, with riders blasting off the start line, but many faced a daunting task staying on their machines.

Nine riders, including championship leader Marc Marquez of Spain on a Suter and rival Italian Thomas Luthi, crashed out heavily. With two remaining races, Marquez leads the championship standings with 283 points. Pol Espargaro has 235 points after clawing five points at Sepang.

Meanwhile,  German KTM rider Sandro Cortese won the Malaysian Motorcycle Grand Prix at Sepang on Sunday to be crowned the inaugural Moto3 world champion.

Cortese started from the front row and raced to the chequered flag in 40 minutes 54.123 seconds over the 18-lap race.

He beat Zulfahmi Khairuddin, who started on pole, on a KTM bike by only 0.028 seconds with the Malaysian rider finishing second.

German's Jonas Folger, who led for much of the race, took third spot after starting from the front row. He was 0.247 seconds behind the winner on his Kalex KTM machine.

The win gave Cortese a 73-point lead over his nearest challenger, Luis Salom of Spain, and with only two races remaining offering a maximum of 50 points Cortese lifted the first Moto3 world title.

Cortese who started from the front row for the ninth successive race, remained calm in third spot for 17 laps and moved ahead of Zulfahmi in the final lap following team orders for the Malaysian to slow down. "I still can't believe I am the world champion," he said.

"I did not race so much. I just wanted to finish ahead of Salom (his closest remaining challenger for the title) but when I saw an opportunity to win the race, I just pushed the bike. It is a dream come true," he added.

The 22-year-old also became the first German rider to win the lightweight class world title since Dirk Raudies in 1993 and the first ever rider to take a road-racing world title for KTM.

Cortese will migrate to the Moto2 class for the 2013 season.

Zulfahmi, 21, became the first Malaysian to secure a podium finish in any class of grand prix racing.

Zulfahmi led in the last seven laps and said he followed team orders to drop to second spot to avoid a possible crash.

Maverick Vinales, who had a mathematical chance of securing the title, did not start the race amid reports that the 17-year-old Spaniard has quit his team.