The Terps added four pitchers that looked like they would help a steady group of returning arms but the staff has struggled so far this season.
Costes' two-run blast energized the Terps during a rainy matchup with the Patriots.
Some late heroics by Kevin Keister, Luke Shliger and Nick Lorusso finished off the Retrievers and lifted the Terps to their 17th win.
The Terps overcame a strong offensive day from the Rams to move to move to 10-2 on the season.
The Wolverines cracked a three-run homer to take the lead from the Terps and never looked back.
The Terps reached 7-0 for the first time in program history, beating the Camels three times in the span of two days to remain undefeated on the season.
Right-hander Elliot Zoellner pitched 3 1/3 scoreless innings of relief, but the Terps faltered late.
Weather forced Thursday's game to continue on Friday morning.
Right-hander Hunter Parsons allowed just one run in 7 1/3 innings.
Lee started 4-for-27, but is now hitting a team-best .301.