By Abhishek Takle

SUZUKA, Japan (Reuters) - Nico Rosberg tightened his grip on the Formula One title race with a dominant victory at the Japanese Grand Prix on Sunday, the German's first win at Suzuka also helping Mercedes claim a third consecutive constructors' crown.

Rosberg, who started on pole, was never seriously threatened and crossed the line 4.9 seconds clear of Red Bull's Max Verstappen, who fended off a late-charging Lewis Hamilton after the Briton recovered from a woeful start to finish third.

Rosberg extended his lead over Hamilton to 33 points in the overall standings following his ninth win of the season and with four rounds remaining, the 31-year-old can claim a maiden title without needing to win another race.

The win was also the 15th of 17 races for Mercedes this season and confirmed three years of dominance, during which time the German outfit has won 47 of 55 races.

"It's been an awesome weekend for sure, the whole weekend had gone great from the word go," Rosberg, who led every session at Suzuka, told reporters.

"Congrats to all my colleagues in the team, for clinching a third constructors' world title.

"Definitely, it's been an unbelievable effort all these years, so let's celebrate hard," added Rosberg, who becomes only the fifth driver in Formula One history to win nine races in a season.

Hamilton went into the race searching for a Suzuka hat-trick to revive his flagging championship prospects after being forced to retire from the lead at the last race in Malaysia but his chances of victory were dashed within a matter of seconds.

The Briton was unable to capitalize on his front-row start as he crawled off the line and found himself languishing down in eighth place by the time he reached Turn One as his Mercedes team mate disappeared over the horizon.

MERCEDES PROTEST

"I made a mistake," said Hamilton, who last won at the German Grand Prix in July prior to the series' annual summer break. "And then just working my way up from there was tricky but I did the best I could."

Once he had recovered from the disappointment of the tardy start, a mix of his trademark spectacular overtaking and clever strategy by Mercedes saw him scythe through the field and very nearly snatch second from Verstappen.

However, the Dutchman held on after rebuffing the Briton's final attempt to pass with a robust move at the chicane on the penultimate lap that sent the Mercedes wide into a run-off area and prompted the German team to lodge an official protest.

That protest, however was later withdrawn, seemingly at Hamilton's request.

"There is no protest from myself. Just heard the team had but I told them it is not what we do. We are champions, we move on. End of!," he said on Twitter.

Ferrari's Sebastian Vettel, who started sixth due to a three-place grid penalty for shunting Rosberg at the start in Malaysia, did well to finish fourth but his hopes of a podium spot were compromised late on by slow moving back markers.

The German got off to a fantastic start and looked competitive in third but after losing touch with Verstappen and getting passed by Hamilton on his second pit stop, a bold tire strategy failed to pay off for Ferrari.

His Finnish team mate Kimi Raikkonen, who started eighth after collecting a five-place penalty for an unscheduled gearbox change, also complained of track-hogging back markers on his way to a fifth-place finish.

Daniel Ricciardo, winner in Malaysia a week ago, was sixth in his Red Bull as Force India pulled further ahead of Williams in their private battle for fourth overall.

Sergio Perez and Nico Hulkenberg finished seventh and eighth ahead of Felipe Massa and Valtteri Bottas, who struggled for pace all weekend but made the most of a one-stop strategy to salvage some points.

(Editing by John O'Brien)