The sophomore advanced to Sunday's final when he opened play on Friday with a three set win (6-2, 4-6 and 10-3) over Pacific's Ben Mirkin.
On Saturday De Jager defeated Jono Knowlman of USF in straight sets, 6-4 and 6-2 and then defeated fellow teammate, freshman Naveen Beasly, in three sets (6-4, 3-6 and 10-7).
Beasly advanced to the semi-final round by opening with a bye in the first round and defeating Pacific's Valentim Goncaves, 6-1 and 6-1, Saturday morning before falling to DeJager.
Marco Comuzzo lost in the round of 16 in the A Flight on Friday to USC's Eric Johnson, 6-7, 6-4 and 6-0. In the consolation round, Comuzzo defeated Will Schumacher of USF, 6-4 and 6-1, before falling in the semifinal round to Oregon's Daniel Sardu 3-6, 6-3 and 10-8.
Other Mustangs competing at the Fresno State tournament included senior Brian McPhee. The senior opened play on Friday with a straight set win, 6-0 6-3, over Nevada's Victor Ouvard, then lost in the round of 16 to Fresno State's Jean Charles Diame 7-6, 7-5.
Junior Jordan Bridge was forced to retire by injury in the round of 32 leading 5-3 in the second set against Sacramento State's Marco Markoo.
In doubles open competition, the duo of Bridge and Comuzzo lost 9-8 to Tommie Murphy and Adnrew Pises from Cal.
In the B Flight of doubles, the team of Sebastian Bell and McPhee advanced to the semifinal round before falling 8-2 to the team of Bahri and Jiganti from USF. Bell/McPhee defeated the team of Mege and Reix from Nevada 8-5 in the previous round.
Beasley and De Jager lost 8-3 in the round of 16 to Josh Albert from UC Davis and Jordan Rozenfeld from Nevada.