Complex sentence: They had an immediate rematch, and on August 21, Jones regained the World Light Heavyweight Title by devastatingly knocking out Griffin in the first round, Griffin had not had the proper time to warm up.
Split into simpler sentences: They had an immediate rematch, and on August 21, Jones regained the World Light Heavyweight Title by devastatingly knocking out Griffin in the first round. However, it was said that Griffin had not had the proper time to warm up.