It's the third time Costes has earned the award this season.
Maxwell Costes and Justin Vought each clubbed three RBIs.
Coach Rob Vaughn was ejected for protesting the Wildcats' go-ahead run in the eighth.
The Terps racked up a season-high 18 hits.
Maxwell Costes and Randy Bednar belted 3-run shots to win Saturday's nightcap.
With the help of sloppy Illini defense, the Terps posted four ninth-inning runs.