A huge partisan crowd estimated at 92,000 was on-hand at Misano World Circuit Marco Simoncelli for the San Marino GP. Valentino Rossi's home track was filled with yellow-clad fans hoping to see The Doctor win his second race in a row. Unexpectedly, Mother Nature took control of the race early and caused havoc with unforecasted rain.

Movistar Yamaha rider Jorge Lorenzo started on pole, having demolished the track record in qualifying. Marc Marquez started in the middle of the front row for Repsol Honda, next to Rossi on the outside.

Lorenzo got off to his usual excellent start, followed by Marquez and Rossi. Drops of rain were seen on the first lap and the white flag was displayed indicating that the riders could change to wet bikes if the weather worsened. No rain had been forecasted for the weekend so the change in the weather was unexpected. None of the teams had ridden on the new track surface at Misano in the wet.

Michele Pirro had problems on the grid and had to start from pit lane; he joined the race on his wet bike at the rear of the field. Unfortunately his issues continued and he returned to his garage with the wet treaded tires shredded as the track was too dry for them.

Rossi set the fastest lap of the race on Lap 3 as he attempted to reel in Marquez and Lorenzo. The red cross rain flag was waved on Lap 6 as the precipitation picked up.

On Lap 6, the front runners came into the pits to switch to their wet bikes. Lorenzo emerged from the pits in first place but was quickly passed by Marquez in the wet conditions. Rossi rejoined the race in third. Marquez ran very wide in Turn 8 on Lap 9 which allowed Lorenzo to regain the lead.

Yonny Hernandez lost control in Turn 6 and took out Alex DeAngelis on Lap 10.

The Yamaha mechanics readied the dry set-up bikes in the pits as the rain continued to fall but a dry line began to appear on the track with 15 laps remaining. Several riders at the back of the field entered the pits and changed back to bikes on slick tires.

Marquez would not let Lorenzo get away and Rossi was able to close up on the front runners. Rossi was able to finally get around Marquez on Lap 14 for second place and closed up on teammate Lorenzo as the crowd roared. Marquez appeared to have handling issues on the drying track as his tires began to degrade.

Rossi took the lead from Lorenzo on Lap 16 and began to pull away as the dry line on the track continued to expand. The riders who changed back to slick tires were turning laps more than nine seconds faster than the leaders on wet tires. With 11 laps remaining, Lorenzo's team displayed the "IN" board indicating that he should come to the pits to switch back to the dry set-up Yamaha.

Marquez entered the pits from third and switched bikes. Rossi's front wet tire appeared to be shredding on the drying track. Neither Yamaha rider came in to change bikes as the laps continued to run down.

With eight laps remaining, Lorenzo switched back to slicks with a medium compound front tire. All riders had switched to slicks before Rossi finally came in on Lap 20 to make the switch.

With seven laps to go, Jorge Lorenzo lost the rear end and had a big crash in Turn 15 and was out of the race. Rossi rejoined the race on slicks in fifth place and was shown "LORENZO OUT" via his pitboard.

On Lap 23, Marc Marquez had more than a six-second lead over second place Bradley Smith. Scott Redding, who early in the race had crashed, battled open class rider Loris Baz for third place, finally passing him with four laps remaining. Rossi contuned to run in fifth place after his late change back to slick tires.

Marc Marquez was able to maintain the lead and score his first career MotoGP victory at Misano World Circuit Marco Simoncelli, crossing the line with a celebratory wheelie. Monster Yamaha Tech 3 rider Bradley Smith finished in second place for his best MotoGP career result and second podium. Scott Redding recovered from an early race incident to score his first MotoGP podium finish.

Valentino Rossi was not on the podium for the first time in the 2015 season, although he was able to increase his championship points lead over Jorge Lorenzo after the Spaniard's crash out of the race. Rossi now holds a 23 point lead over his teammate as the series heads to Aragon in two weeks.

In Moto2 action, Ajo Motorsport rider Johann Zarco scored his sixth victory of the season and extended his points lead to 93. The Frenchman stood on the podium for the 12th consecutive race and can mathematically claim the title at Motegi. A total of six riders crashed out during the race. Zarco was joined on the podium by Tito Rabat and Takaaki Nakagami.

Gresini Racing Team Moto3 rider Enea Bastianini won his first Moto3 race in a close battle with Miguel Oliviera and Niccolo Antonelli. Points leader Danny Kent finished sixth and was forced to give up position after exceeding track limits at Turn 6 several times. He holds a commanding 55 point lead going into the next race.

Next up for the MotoGP World Championship is the Grand Premio Movistar de Aragon at Motorland Aragon in Spain in two weeks.

Follow @VAVELMotoGP on Twitter for coverage leading up to and during the Aragaon weekend.

Cathy Shumaker is a writer for the VAVEL USA Racing section. Follow her on Twitter at @cathyshu.