Kiritsugu is a pretty skilled mage. He’s able to fight at close range combat rather well thanks to his time manipulation. Additionally he’s a solid shot and can fire bullets which disrupt magic. None of that will be able to stop a man of Phoenix Ikki’s caliber though. The guy will simply burn his cosmos all the brighter. His Fire blows can burn through anything Kiritsugu tries to throw his way and he’s also a lot faster in general. As a result, there’s just nothing Kiritsugu can really do to defend himself here. Phoenix Ikki wins.