Having been outshone in their opening night defeat to Finland, scoring just 10 points, the Miami Heat guard missed last night's heavy loss to Germany through illness.
But both Larsson and Simon Birgander recovered in time for this afternoon's clash which was already verging on "must-win" for both sides, as Great Britain had also suffered two losses from their first two matches in the group.
Both players were off the mark quickly as Sweden opened up a 12-6 lead midway through the first period, while steals from Melwin Pantzar and Denzel Andersson set the tone defensively, as the Swedes maintained that six-point advantage until the end of the first quarter, 19-13.
An 8-0 run to begin the second quarter was ideal for Sweden, but having taken a timeout, GB regrouped and Luke Nelson and Jubrile Belo found their range from beyond the arc to reduce the deficit.
What was a 14-point lead at more than one stage was down to five at the half, thanks largely to a 9-3 British run to end which was finished off by a Jelani Watson-Gayle three-pointer on the buzzer to really give Marc Stuetel's side real belief.
Having edged the second quarter 17-16, Great Britain scored 17 points again in the third, only this time they failed to deal with the Swedish attack, which notched 26 as Larsson took his nation's destiny into his own hands.
The 24-year-old scored 14 points in those 10 minutes alone, eight of which came in an 11-3 run as Sweden opened their biggest lead of the game so far - 16 points - then he added three more with the final possession to take his side 61-47 ahead.
Sweden could have won the game without scoring in the final quarter, as their defence allowed just 12 points in the last 10 minutes. Fittingly, it was Larsson who added two more to extend the lead to 20 points, before the final buzzer sounded with the Scandinavians 78-59 ahead.
Myles Hesson top scored for Great Britain with 17 points, while Carl Wheatle notched an impressive 13 rebounds, five more than Pantzar. Birgander led the assists with six, as Pantzar led the game with four steals.
The win takes Sweden to fourth in the group, ahead of Great Britain and Montenegro, which is where they will have to stay if they want to progress to the knockout stages, with Monday's meeting with Montenegro a crucial game.