Complex sentence: Mickelson made eagle on the seventh hole to tie for the lead and added a birdie on 10 to move to 6 under for the day; but Clarke, three groups behind, countered with his own eagle on the seventh to open up a two shot lead.
Split into simpler sentences: Mickelson made eagle on the seventh hole to tie for the lead and added a birdie on 10 to move to 6 under for the day. Clarke countered with his own eagle on the seventh hole to open up a two shot lead.