Something that Anakin accomplished rather easily? Was the former because Obi-Wan had to play aggressive because Anakin was leading the attack.
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He knows Anakin's lightsaber-fighting style better than Dooku's.
And the higher ground advantage at the end of the duel.
It was Obi-Wan’s experience (and Anakin’s recklessness) that led to him besting Anakin. Once he got the high ground, it was over.
shareThe Jedi numbers were severely depleted by that stage.
Remember the sith "rule of two" means that all the dark side midi-chlorians are only shared out by only a couple of force users. Conversely the balancing number of light side midi-chlorians have to be shared out among many, many Jedi.
By the end of the film though, there are hardly any Jedi left and therefore Obi-Wan can call upon a lot more midi-chlorians than at the start. In fact there are only two of them left and we see Palpatine and Yoda (the other Jedi) battle out an almost even draw.
Therefore, scientifically speaking, it stands to reason that they should have been more or less evenly matched...