Costly helps Honduras crush Costa Rica
Veteran Carlos Pavon was also on target as the Hondurans jumped up to second in the final stage of the region's qualifying tournament, two points behind their opponents.
Costly, who scored twice in the 3-1 home win over Mexico and notched the winner against El Salvador, opened the scoring in the 31st minute, converting a pass from Pavon, and completed the rout with a stoppage time goal.
In between, 35-year-old Pavon scored in the 51st minute after collecting the ball with his back to goal, turning and firing a shot past Ricardo Gonzalez.
Melvin Valladares added the third in the 90th minute.
Costa Rica stayed top of the six-team group on 12 points from six games and Honduras moved ahead of the United States on goal difference.
The top three teams qualify directly for next year's World Cup in South Africa and the fourth plays off over two legs against the fifth team from South America.