But the battle of the race was for second place, as Felipe Nasr pipped James Calado for the position in the very last few yards, outdragging him with superior traction out of the final chicane after an enthralling late duel.
"It was quite amazing, I was just waiting for the last moment," said Nasr.
Calado added: "A fantastic race, really. I got a lightning start, seventh to nearly first. I had good pace, but it was tough to keep with [Kral] and save the tyres. The last three laps were evil, it was unstable under braking."
Third-placed Calado made inroads into points leaders Davide Valsecchi and Luiz Razia after a controversial moment on the opening lap.
Having made a good exit from the first corner, third-placed Razia got a better run onto the Kemmel Straight than Calado, who appeared to leave him no room and force him onto the grass at 150mph as the Brazilian pulled alongside.
This sent Razia spinning across the track - in front of the majority of the pack - but amazingly he only took out one other car.
Ironically, this was Valsecchi, the man with whom he is tied with at the top of the points table. Valsecchi clanged into the barrier on the inside of the track, but both continued after a significant delay. Valsecchi had already come together with Giedo van der Garde and Julian Leal in one of several La Source tangles.
The stewards investigated the incident, but took no action during the race.
Valsecchi would retire after nine laps, while the chastened Razia trailed home in 20th. They remain locked on 204 points at the head of the table, with Calado 44 behind.
The fourth man in the title battle, Esteban Gutierrez, failed to score after an ill-judged move on Leal for fourth place meant he spun into the gravel at Malmedy. He rejoined to finish 13th.
Kral won by 5.1 seconds, his first-ever GP2 success and only his second points-scoring result of the season after he finished fourth on Saturday.
"We have been waiting for this, it's been really tough, I've had so much bad luck," said Kral. "Today it was just perfect, and yesterday was good as well - 14th to fourth. The tyre degradation was really bad, I was sliding a lot."
Saturday's winner Marcus Ericsson charged from eighth to fourth, but the star of the race was Fabio Leimer, who rose from 23rd on the grid to fifth.
The highlight of his quite brilliant drive was passing Fabio Onidi flat-out around the outside of Blanchimont.