Fielding the same squad just four days after losing the tournament opener by 20 to Japan hurt the Russians, who were game but ran out of energy. The Bears ended up missing 44 tackles as Manu Samoa, fresh in their first game of the tournament, made 11 breaks and ran free in the second half where they scored five of their six tries.
"It wasn't a physical deterioration, it was mental," Russia coach Lyn Jones said.
Samoa drew the first points attacking from a lineout. Fullback Tim Nanai-Williams gave an overlap to right wing Alapati Leiua who stepped the cover and was in.
But Russia came back with penalties by flyhalf Yuri Kushnarev to lead 6-5, and Samoa reacted badly.
In a two-minute span, center Rey Lee-Lo and hooker Motu Matu'u were sin-binned for shoulder-led hits at the head of Russia fullback and captain Vasily Artemyev. They weren't red cards from French referee Romain Poite because both times Artemyev ducked down to brace for impacts.
Samoa coach Steve Jackson said the problem wasn't discipline but tackle technique.
"We didn't learn from last weekend with people being cited," Jackson said. "We've got to be better in that area."
Russia couldn't make the two-man advantage pay, being forced back into its own half. Not until right near halftime, when Samoa had 14 men, did Russia threaten, and only after Nanai-Williams spilled a high ball inside his 22 to put his team under pressure.
Flyhalf Tusi Pisi was charged down by Vladimir Ostroushko and the ball fell in goal about a foot in front of his despairing dive. Pisi then had to make a try-saving tackle on lock Bogdan Fedotko, who spilled the ball within touching distance of the tryline.
Russia, playing a Pacific Island side for the first time, incredibly led into halftime, but the lead evaporated within five minutes of the interval.
A sweeping move full of offloads put Samoa No 8 Afaesetiti Amosa over the line, but only after he was hooked around the neck by Russia prop Kirill Gotovtseva. Amosa twisted his right knee and had to be carried off without seeing Gotovtseva issued a yellow card.
Samoa had the lead back at 10-6, though it would have been more if Pisi, Samoa's oldest World Cup player at 37, was more accurate off the tee.
Kushnarev showed him how with a cool dropped goal to cut the deficit to one, but Russia was 14 men down and flagging and Samoa was energised by more fresh legs off the bench.
A no-look pass by replacement hooker Ray Niuia put winger Ed Fidow through the defense and around behind the posts to give Pisi an easier shot at goal.Then just four minutes later, Fidow's second try — and 10th in nine tests — earned Samoa a bonus thanks to an overlap pass from Leiua.
Lee-Lo scored the fifth try from a lineout attack with the final pass from Pisi, and after holding out a sustained 10-minute attack from the Russians, Samoa rubbed it in with a sixth try from a scrum on halfway. Leiua fended off one defender and high-stepped out of another to score his second try, and Pisi landed his second goalkick from seven attempts.
Both teams travel to Kobe. Samoa plays Scotland on Monday, while Russia has a nine-day break before facing Ireland.