Complex sentence: The next two players from each league with the most homers squared off against one another in a head-to-head matchup in the second round, from which the winners advanced to the third round to compete against the league's top seed.
Split into simpler sentences: The next two players from each league with the most homers will square off against one another in a head-to-head matchup in the second round. The winners of these matchups will advance to the third round to compete against the league's top seed.