Thompson, the tournament's No. 1 seed, was able to recover after losing the first set to the third-seeded McDonald in Sunday's singles final, eventually coming back to win 3-6, 6-3, 6-4. It marked Thompson's second title at the Southern California Intercollegiates, also winning the event in 2011.
Despite the loss in singles, McDonald still managed to win a title on Sunday, teaming with Sell to post an 8-4 win over teammates Joseph Di Giulio and Ryoto Tachi in the men's doubles final. McDonald and Sell were seeded No. 2 in the 16-team draw.
The two titles on Sunday gives UCLA three championships at the event, as Bruin Seth Stolar took home the consolation singles crown on Saturday.
Complete results from the tournament can be found on the USTA's Southern California Intercollegiates website.
Doubles Final (Sunday)
(2) McDonald/Sell (UCLA) def. Di Giulio/Tachi (UCLA) - 8-4
Consolation Singles Final (Saturday)
Seth Stolar (UCLA) def. Caryl Hernandez (UCI) - 6-3, 6-4
Doubles champions Mackenzie McDonald and Karue Sell with finalists Joseph Di Giulio and Ryoto Tachi