The judges had it 118-109, 116-111 and 116-111 for Klychko, who lost a point for holding in the 10th round. Klychko was cheered wildly by a crowd filled with fans waving Ukrainian flags.
For the fight, Klychko landed 144 of 545 punches (26 percent) and Jennings landed 110 of 376 (29 percent).
"Very competitive opponent, [better] than I have faced in recent years. Great hand speed, great footwork, very athletic. He gave a great challenge and he will give the heavyweight division a lot of good challenge," Klychko said.
Klychko's 18 consecutive defenses of his second title reign are third all-time in division history behind only Larry Holmes (20) and Joe Louis (25, which is the all-time record for any weight class).