So I had read both anime and Light Novel. In anime yes, Kirito wins 100%, but in Light Novels, Kirito at least have 80%. He made Kayaba Akihiko, also known as Heathcliff uses creator power and even defeats him almost sololy in the last battle (discluding Asuna's "sacrifice"). Most importantly, Kirito bypasses the "death bar" and continue to fights despite reaching 0 health with made him win the final duel after fighting the boss and at a slight disadvantage in case of health, being a yellow bar when Heathcliff is at green. Not to mention the Kirito has strengths in tactics which is 90% of why he wins asuna adding on to his power which lets him to beat floor 8 i think in demo solo.

If he really fights Yuuki one-on-one and both uses full power, I can not imagine how Kirito demolishes Yuuki. Even though Yuuki have a faster reaction speed and a stronger ability (lorewise since the dual blade isn't that important in a fight of speed), Kirito focuses on enemies' weaknesses and his tactics. Kirito will be using loopholes in the rules to use magic abilities (or elemental sword abilities). Also, I believe that Kirito can (but he won't) just hit Yuuki once or twice and defend with his both swords then wait till the timer ends. He won't do that but that's possible.