Navy committed 19 second-half turnovers and watched as defending Patriot League champion Lafayette caught fire from the foul line as the Leopards dropped the Midshipmen, 80-74, before 2,882 at A. P. Kirby Sports Center.
With the game tied at 72, Lafayette's Brian Ehlers made two free throws and sank another to give the Leopards the lead, 76-72. After a jump shot by Navy's Chris Williams, Lafayette's Tim Bieg ensured the win from the foul line.
After Bieg hit a free throw to extend the lead to three, Williams quickly drove downcourt but missed a 12-foot leaner with 12 seconds left. Bieg sank 1 of 2 free throws to increase the margin to 78-74 with 9.7 seconds left.
With two possessions and an outside chance, Navy lost any shot at a comeback when Josh Hill's outlet pass was stolen near midcourt. Bieg made two more foul shots for the final score.
Navy's defense helped the team get off to a quick start, holding Lafayette to three field goals in the first 11 minutes as the Midshipmen built a 22-10 lead.
But once the Leopards found a way to get the ball to 6-foot-11 center Stefan Ciosici, they got back into the game. Lafayette dumped the ball inside for two quick layups by Ciosici and cut the Navy lead to 40-34 at halftime.
Navy shot 59 percent in the first half, hitting 10 of its final 11 shots.
"This wasn't the 40-minute game we needed to beat Lafayette," Navy Coach Don DeVoe said. "We just made far too many mistakes."
Turnovers were costly for Navy, which committed a season-high 29 and was outscored from the foul line 25-8. The Midshipmen (10-5, 1-1) shot 53 percent from the field, but their five-game winning streak came to an end.
Lafayette (9-5, 1-1) had entered the day shooting 72 percent from the foul line.
"I thought it was two different halves," Lafayette Coach Fran O'Hanlon said. "They took it to us in the first half, but in the second half we turned up the defensive intensity."
Williams and center Sitapha Savane (16 points) were a combined 16 for 25 from the field, with Williams hitting all three of his three-point attempts. But Ciosici, who scored 14 of his game-high 23 points in the first half, was the difference.
"We elected to guard the three-point shooters, and Ciosici had a field day," DeVoe said.