In Group C, Peter Podhradsky scored twice to lead Slovakia to a 5-1 win over Germany and a place in the qualifying round, while Switzerland joined Sweden advancing out of Group A with a 2-1 victory over Italy.
Backstrom was one of eight different players to score for the defending world and Olympic champions, who improved to 2-0.
Jorgen Jonsson passed from behind the net to Backstrom, who beat Latvia goaltender Edgars Masalskis before many of Sweden's fans had settled into their seats.
"It felt good to get that early goal," said Backstrom. "Our line didn't play that well in the first game but we're starting to get some good chances and hopefully we can keep it up."
Despite having only one player from the NHL on its roster, Sweden has outscored its first two opponents by a combined 15-3.
"This was a good win for us," coach Bengt-Ake Gustafsson said. "It was much harder than the game versus Italy. We were scared all the time when Latvia was in our zone. Skill-wise, we are the same as last year, but we need to fine-tune the defence."
Johan Akerman, Rickard Wallin and Fredrik Bremberg added second-period goals to give Sweden a 4-0 lead.
Latvia scored twice in 91 seconds early in the third to cut the lead to 4-2 but Backstrom set up Magnus Johansson, who beat Masalskis with a slapshot from just inside the blueline to make it 5-2 at 3:08 of the third.
Patric Hornqvist, Fredrik Warg and Dick Tarnstrom scored later in the third to complete the rout for Sweden.
Backstrom elected to play in the Swedish Elite League this season instead of joining Alexander Ovechkin in Washington. He is widely regarded as the most talented player to come out of Sweden in many years.
Slovakia, the 2002 world champion, scored only once in the opening period when Podhradsky shot a loose puck between Oliver Jonas' pads during a power play.
However, the Slovaks got a boost from new additions Marian Hossa, Marian Gaborik and Pavol Demitra, who were all added to the roster Monday.
Gaborik, recovering from a virus, and Hossa, shaking off jet lag, combined for a spectacular goal.
Gaborik stormed down the boards, leapt over a prone German defenseman and fed Hossa. The Atlanta Thrashers forward then rushed the net, faked Jonas with a quick short pass to the left, which Gaborik banged in to make it 4-1.