The Bears fell behind early 20-11 after the opening quarter.
But a strong Bears defensive effort kept it close for a narrow stretch.
Summerville limited Argonaut to a game-low 13 points in the second period, and the Bears dropped 17 points during that time to enter the break down 33-28.
However, that stout defensive pressure was short lived, and Argonaut outscored Summerville 28-6 to pull away in the third quarter.
“They were hitting some shots,” Watson said. “They were pounding the boards. They got second-chance opportunities. They also broke our press. They just went on a run where they got hot. At the same time, we didn’t. We just didn’t do a good job on the boards. We didn’t battle real hard. On top of that, we weren’t hitting our shots.”
Despite a below average outing to start the second half, the Bears rebounded in the final 8 minutes.
Summerville dropped 25 points in the fourth quarter and held Argonaut to just 15.
Sophomore guard Danny Robles netted six of his 11 points in the final period, and Ethan McLaurin led the Bears in scoring, finishing with 12.
“Danny Robles had a good fourth quarter,” Watson said. “He played hard.”
The Bears (4-8, 0-1 MLL) will host their first home game in over a month when they tip off against the Bret Harte Bullfrogs at 7:30 p.m. on Tuesday in Tuolumne.
“We just got to play better defense and really got to improve our rebounding,” Watson said. “It’s an attitude thing. We have to, everybody on the team, we have to rebound as one. We have the capability, I just don’t think we’re focused right now. We have two home games this week. We need a lift right now. We have to get something going.”