The Battle of Utapau was a conflict that took place near the end of the Clone War, after the CIS conquered the sinkhole-world of Utapau. Republic agents received word that General Grievous had set up shop on Utapau and dispatched a clone attack force led by Obi-Wan Kenobi to kill him. Grievous had evacuated the Seperatist Leaders from the planet not long before and was readying himself to leave as well when Obi-Wan Kenobi dropped down from the rafters of his base and attacked him.
After a lengthy duel that encompassed a large chase through the sinkholes of Utapau, Kenobi was finally able to put Grievous down with a blaster as the Clone Troopers moved in to attack. Leaderless and disorganised, the Seperatist forces were quickly overpowered and most were destroyed within a few hours. However, as the battle was starting to turn in the Republic's favour, Order 66 was executed by Darth Sidious, and the Clone Troopers fired upon Obi-Wan Kenobi, causing him to fall into a sinkhole. Presumed dead, the Clones left him there in the water.
However, Kenobi was not dead and he was able to escape in Grievous's personal starfighter and was picked up by the Tantive IV, which had Yoda and several Senators on board, and they made plans to counter the betrayal of Palpatine.