Maritimo had Moussa Marega and Raul Silva sent off in the second half, while Guimaraes' Andre Andre had a penalty saved after the second red card, as Rui Vitoria's side triumphed 1-0 at home.
Guimaraes had not won since their Taca da Liga triumph against Belenenses on February 4, while their last league victory came in January - a 4-0 thumping of Academica.
But Josue Sa's looping header from Alex's free-kick in the 34th minute was enough for Guimaraes to claim three points on Friday, although they should have scored more against their undermanned opponents as they finished the match with 12 shots to six.
Marega, who had received his first yellow card in first-half stoppage time, was given his marching orders two minutes after half-time and Silva suffered the same fate with four minutes remaining.
Silva slipped in the penalty box and took out Guimaraes substitute Sami but Andre failed to convert from the spot as goalkeeper Romain Salin made a save to his right.
The win took Guimaraes to 40 points to sit fifth in the standings, the Primeira Liga's second UEFA Europa League berth, six points clear of sixth-placed Belenenses and three behind Sporting Braga, who are fourth.
