We can't tell who is KOed by the spoilers, BUT, if Zoro states "I did all I can. I leave the rest to you" and Law is alive, that clearly implies Law > Zoro.
Zoroo was about to the final attack, he was his limit, trying to use his full power. In the end both going down, with Zoro was the only one who perform a insane feat.
It doesn´t mean Law was stronger, Zoro was about to go all out, in fact Law was take thunder bague in the end too without doing anything special.
While Zoro:
Cut Kaido twice, give him big wound, use adv CoC, block hakai and endurance the attack.
That is beyond anything with Law show.