Three tries in eight minutes at the start of the second half saw Samoa overcome a slow start and earn a bonus-point win against spirited Russia.

The Pacific Islanders went down to 13 men in the first half as Rey Lee-Lo and Motu Matu'u were both sin-binned for high tackles on Vasily Artemyev.

Russia led at the break thanks to two penalties from Yury Kushnarev.

But Samoa found their fluency to run in five second-half tries and ease to victory as the Bears ran out of steam.

Samoa narrowly top Pool A - which also contains hosts Japan, as well as Ireland and Scotland - on points difference.

Russia were on top in the early stages at Kumagaya Stadium as Samoa were slow to find their feet, but it was the latter who opened the scoring through Alapati Leiua's try.

The Bears responded well and two penalties from Kushnarev put them into the lead in the 25th minute.

Samoa then received two yellow cards in three minutes when Lee-Lo and Matu'u were sent to the bin by referee Romain Poite.

In both instances, the players appeared to make contact with Russian skipper Artemyev's head, but Poite deemed that he was dipping into contact and that yellow cards were sufficient.

Samoa hit the ground running in the early stages of the second half, with Afaesetiti Amosa's score and a quickfire Ed Fidow double taking the game away from Russia.

Lee-Lo and Leiua's second wrapped up the scoring, with Russia held up on the line as they pressed in vain for a consolation try.

Samoa now face a crucial tie against Scotland on Monday (11:15 BST) in Kobe, whereas Russia meet Ireland in the same city on Thursday, October 3 (11:15 BST).

Russia coach Lyn Jones:

"It's very disappointing. The performance wasn't what we expected. However, the short turnaround has affected us tactically and mentally.

"I thought we could play the same tactics as Japan, but it wasn't going to be tonight. We needed more time to prepare.

"It's not the physical deterioration, it was the mental. We just weren't there tonight."

Samoa coach Steve Jackson:

"To lose two players, go down to 13 men and we didn't lose on the score, I'm really proud of the effort.

"We knew we would come out after half-time and the boys were still fresh. I'm just glad we got over the line."

Russia: Artemyev (capt); Davydov, Ostroushko, Gerasimov, Golosnitskiy; Kushnarev, Dorofeev; Morozov, Selskii, Gotovtsev, Ostrikov, Fedotko, Zhivatov, Gadzhiev, Vavilin.

Replacements: Matveev, Polivalov, Bitiev, Garbuzov, Sychev, Perov, Gaisin, Sozonov.

Samoa: Nanai-Williams; Leiua, Lee-Lo, Taefu, Fidow; Pisi, Polataivao; Mulipola, Matu'u, Alaalatoa, Paulo, Le'aupepe, Vui (capt), Ioane, Amosa.

Replacements: Niuia, Alo-Emile, Jordan Lay, Toleafoa, Tyrell, Matavao, Alatimu, Seuteni.

Referee: Romain Poite (Fra).