FIFA World Cup
Aston Villa captain McGinn fired in with the aid of a deflection just before the half-hour mark at the Gillette Stadium just outside Boston, which was filled to its 64,000 capacity with a majority of Scottish fans.
They have travelled to the United States in large numbers to follow Scotland's first World Cup campaign since 1998, and were able to celebrate a rare victory at the tournament as they go top of Group C.
McTominay almost gave a Scotland team playing in salmon pink the lead in the 17th minute, when he arrived at the edge of the area to crash a shot off the post from a Ben Gannon-Doak lay-off.
Haiti were beginning to grow as a threat when Scotland took the lead on 28 minutes.
Che Adams stretched the opposition defence before Gannon-Doak's ball in fell to McGinn, and his shot found the net via the outstretched leg of Bellegarde.
They were unable to build on that, as Haiti forced them back and stepped up the pressure in the closing stages as they sought to avoid defeat in a World Cup game for the first time.
French-born Ruben Providence was a regular threat on the wing and imposing centre-forward Frantzdy Pierrot almost equalised in the 85th minute, but his towering header went just wide.
Steve Clarke's team are bidding to make history by reaching the knockout stages, something Scotland have never done at the World Cup.
They had to hang on grimly at the end, but the victory puts them on course to get to the last 32, especially as the eight best third-placed sides will go through from the group stage.
Scotland play Morocco at the same stadium in their next game on Friday before heading to Miami to take on Brazil. Morocco and Brazil drew 1-1 in Saturday's other Group C encounter in New Jersey.
Haiti, who lost all three games in their only previous World Cup appearance in 1974, now face Brazil next in Philadelphia.
Sources: AFP, FIFA via Getty Images
