Ferrari's Felipe Massa became Lewis Hamilton's closest championship challenger with a deserved victory in the European Grand Prix at Valencia on Sunday.

The Brazilian held off the challenge from Hamilton's McLaren throughout the race on the new Spanish street track.

Massa dominated but his win is under threat after he was released into the path of another car after a pit stop.

BMW Sauber's Robert Kubica was third, while Ferrari's Kimi Raikkonen saw his title hopes dented with retirement.

Hamilton's lead is a point bigger than it was at the start of the race - he now leads by six points from Massa, while Raikkonen's deficit following his engine failure has grown from five points to 13.

But Massa may yet lose his victory because the stewards are investigating an incident at his second pit stop, when he was released illegally into the path of Force India's Adrian Sutil.

Unusually, the stewards decided they would investigate the incident at the end of the race - a move that will be met with cynicism in the F1 paddock given the potential impact on the title battle.

It may have been influenced by Ferrari's pit-stop system, in which the team do not have a "lollipop man" controlling the driver.

Instead, they use a system of lights, which are operated by the crew doing the pit stop.

Out on the track, Massa and Hamilton staged their own private battle at the front of the field, but the Ferrari driver was always just that bit too fast for his rival.

Massa consolidated his pole position into a lead on the first lap as Hamilton, starting on the dirty side of the track, was forced to defend his second place from Kubica.

Massa then proceeded to edge away from Hamilton until he had a lead of nearly five seconds by the time of his first pit stop on lap 15, two laps earlier than Hamilton's first stop.

But despite two superbly quick laps from the McLaren driver before he came into the pits, the margin between the two was reduced by only a second when Hamilton rejoined.

And Massa was even stronger in the second stint, pulling away from Hamilton in a more convincing fashion to be more than eight seconds in front by the time of his second stop on lap 37.

The Ferrari driver regained his lead when Hamilton stopped two laps later and cruised to his fourth victory of the year - the same number as Hamilton.

"I can't complain with second place," Hamilton said.

"We've had quite a strong weekend. I've had a traumatised weekend - I've had a problem health-wise.

"But we got some good points this weekend and so it was solid for us.

"I got a reasonably decent start but I just had to try and hold my spot but after that I was able to relax and try and attack and keep up with Massa.

"I thought we would keep a certain gap and maintain it but he just stretched it."

Massa was thrilled to make up for the disappointment of losing a win in the last race in Hungary when his engine failed with three laps to go.

"It's amazing after such a bad result," he said. "We've come here to a new track and did a fantastic job; preparing the car in the sessions and choosing the right tyres, which was pretty difficult.

"Then making the pole and winning the race and making the fastest lap there is nothing more we can ask for."

Provisional result from European Grand Prix at Valencia:

1. Felipe Massa (Brz) Ferrari one hour 35 minutes 32.339 seconds
2. Lewis Hamilton (GB) McLaren-Mercedes at 5.611secs
3. Robert Kubica (Pol) BMW Sauber at 37.353
4. Heikki Kovalainen (Fin) McLaren- Mercedes at 39.703
5. Jarno Trulli (Ita) Toyota at 50.684
6. Sebastian Vettel (Ger) Toro Rosso- Ferrari at 52.625
7. Timo Glock (Ger) Toyota at 1:07.990
8. Nico Rosberg (Ger) Williams-Toyota at 1:11.457
9. Nick Heidfeld (Ger) BMW Sauber at 1:22.177
10. Sebastien Bourdais (Fra) Toro Rosso-Ferrari 1:29.794
11. Nelson Piquet Jr (Brz) Renault 1:32.717
12. Mark Webber (Aus) Red Bull-Renault one lap behind
13. Jenson Button (GB) Honda one lap
14. Giancarlo Fisichella (Ita) Force India-Ferrari one lap
15. Kazuki Nakajima (Jpn) Williams-Toyota one lap
16. Rubens Barrichello (Brz) Honda one lap
17. David Coulthard (GB) Red Bull-Renault one lap
R Kimi Raikkonen (Fin) Ferrari 45 laps completed
R Adrian Sutil (Ger) Force India-Ferrari 41 laps completed
R Fernando Alonso (Spa) Renault one lap completed

R = retired