Complex sentence: Lewis opened a cut above Klitschko's eye with a right cross in the third round and gave a better showing in the fourth round, and gaining the upper hand in fifth and sixth rounds.
Split into simpler sentences: Lewis opened a cut above Klitschko's eye with a right cross in the third round and began to force his way into the fight. He gave a better showing in the fourth round, and gaining the upper hand in fifth and sixth rounds.