Grenada also recovered from its opening day loss to beat Guyana 2-1, leaving it and French Guyana atop second-round qualifying Group 6 with four points, one ahead of Haiti with one match to play. Guyana, which lost its second straight and had zero points, was eliminated.
French Guyana will finish its Group 6 play on Sunday against Guyana, while Grenada and Haiti will face off. Two teams will advance to the Caribbean Cup finals in Antigua & Barbuda in December. Four teams will qualify from the Caribbean Cup for next year's CONCACAF Gold Cup.
Pigree's goal in the 55th minute was his seventh in four games in the past five weeks of Caribbean Cup qualifying and ended Haiti's five-winning streak.
In the second game of the doubleheader, Clive Murray scored in the 81st minute to end Grenada's five-game winless streak. Kithson Bain gave the "Spice Boys" the lead in the opening minute of the second half, but Daniel Wilson equalized two minutes later.
The win was Grenada's first since a 4-1 World Cup qualifying victory in October 2011, and only its second over 19 games in nearly two years.
French Guyana needs only a draw against Guyana on Sunday to advance to the Caribbean Cup finals for the first time since 1995. In the other game, Grenada will face Haiti for the fourth time in their history, with the Haitians having won all three previous meetings.