Cambridge had pulled ahead at the start and had a half-length lead at the mile mark despite a clash of oars. They then quickly extended their advantage to four seconds when they passed under the Hammersmith Bridge.
"On the start I thought: 'I've missed this'," Cracknell told the BBC. "The first few minutes were great but they just didn't drop.
"To be honest the endurance wasn't a problem. If I had any doubt it would have been my sprinting. I just made sure I stuck it in and hopefully we had enough in the bank."
It was a victorious return to the water for Cracknell, who had retired from competitive rowing in 2006 but qualified for the event because he is studying for a Master of Philosophy degree in human evolution at Cambridge.
Cambridge also comfortably won their third successive women's race earlier in the day with a time of 18 minutes 47 seconds, 17 seconds ahead of Oxford.
Cambridge's men extended their head-to-head record to 84-80 while the women lead 44-30.
(Reporting by Rohith Nair in Bengaluru; Editing by Toby Davis and Clare Fallon)
