[Jimmy McCorkle for Shaw Media]
Chase Thumm's free throw with 23.8 seconds left in regulation forced overtime, but from there more of Marquette's 16 turnovers kept the Crusaders scoreless for almost three minutes.
Lunford's basket boosted Yorkville Christian to a five-point edge, and solid free-throw shooting the rest of the way sealed the Mustangs' win.
"You have to give Yorkville Christian credit. There at the end, they really go after it and did a nice job. They beat us and they deserve to go on," said Marquette coach Todd Hopkins.
Yorkville Christian freshman Jaden Schutt, who scored 12 points, hit two first period 3-pointers to get Yorkville Christian out to a 21-14 lead.
Schutt picked up his third foul with 3:18 left in the second quarter, and the tandem of Thumm and Mullen led a 16-4 Marquette surge bridging the second and third quarters.
Marquette managed to maintain a slim lead until a huge pair of 3-pointers by Couch, the latter creating a 56-51 margin at the 1:57 mark of the fourth.
But the Mustangs rallied behind a defense that forced the Crusaders to shoot more from the outside and Lunford, the last two of his 12 points in the quarter coming off a turnover with 46.9 seconds to go in the fourth setting up a go-ahead basked by Colton Schutt.
"You have to pick your poison with them," Hopkins said. "The last time we faced them, [Colton Schutt] and [Tristen Phillips] did a lot and with the freshman [Jaden Schutt] coming back, they spread you out and play pretty much like five guard, with [Lunford] an off-guard. He hurt us scoring and on the boards. He had a real nice game for them.
"It really hurt us falling behind early. You have to expend so much energy getting back in it, it takes a toll. We played pretty solid defense, but they're just so darn quick ... The ball just didn't bounce our way at the end and we just came up short."