The Toreros (12-6, 2-1 West Coast conference) have won three straight and 10 of their last 12.
The Lions (8-12, 0-4) have dropped seven straight and are winless in the conference.
LMU nearly overcame a 16 point second-half deficit, with Damian Martin's basket with 19.6 seconds left cutting the Toreros' lead to 77-74.
But DeRogatis made one of two free throws with 18 seconds remaining, the Lions missed two shots on their final possession and San Diego held on to win.
DeRogatis had six 3-pointers and had six assists. Pomare, the conference leader in rebounds, led the Toreros with eight boards. Johnson, the conference leader in assists, dished out five assists.
Adoyah Miller tied a career-high in scoring and led the Lions with 23 points, including six 3-pointers. Martin made eight of 11 shots and scored a career-high 18 points. He also had seven assists.
The Lions committed 10 turnovers in the first-half.