The U.S. were 2-0 up and coasting after seven minutes but a dogged Belarus side pegged them back to 2-2, keeping pace for almost two full periods before falling away and eventually losing.
Nate Thompson of the Tampa Bay Lightning got the go-ahead goal, putting the U.S. 3-2 up when he rounded the net and fired in off a defender's skate.
Bobby Ryan and Paul Stastny put the U.S. out of sight with two third-period goals before Belarus pulled one back in the dying seconds. The U.S. have now had three wins and a defeat.
Finland fired four goals in the second period on the way to a thumping victory against France earlier on Thursday at Hartwall Arena in Helsinki.
The French were the authors of their own downfall as they were punished four times for power play goals by a rampant Finnish side that has won all four of its group matches so far.
Russia beat Denmark 3-1, with all the goals coming before the half-hour mark, in Thursday's first Group S clash in Stockholm.
Czech Republic saw off the challenge of Latvia as they coasted to 3-1 victory in the evening game.
That result saw the Czechs leapfrog the Latvians into third place behind Sweden and Russia who both have perfect records after four games.