RIYADH, Saudi Arabia — Oleksandr Usyk has been shorter, lighter and older than all of his opponents since he moved up to the heavyweight division.

Usyk’s heart and skill are enormous, and he overcame a major size disadvantage against Tyson Fury to become the world’s first undisputed heavyweight boxing champion in 24 years.

Usyk defeated Fury by split decision on Sunday, knocking down his hulking opponent in the ninth round and eventually earning a narrow win on two scorecards. The 37-year-old Ukrainian is the first heavyweight to hold every major title belt since Lennox Lewis.

Usyk (22-0) added Fury’s WBC title to his own WBA, IBF and WBO belts with a spectacular late-round rally in a back-and-forth matchup between two previously unbeaten champions from a strong era of heavyweight boxing. Two judges favored Usyk, 115-112 and 114-113, while the third gave it to Fury, 114-113.

“It’s a great time. It’s a great day,” said Usyk, who is 6 inches shorter than Fury and weighed in 30 pounds lighter this week.

Usyk started quickly, but then had to survive while the confident, charismatic Fury dominated the middle rounds. Usyk surged in the final rounds, just as the Olympic gold medalist has done so many times in his career, taking control with a dominant eighth and nearly stopping Fury in the ninth.