Phelps pips rival Cavic in heats

Michael Phelps pips Serbian rival Milorad Cavic to qualify second fastest for the 100m butterfly final.

The duo' s rivalry extends back to the Beijing games where it looked like Cavic was going to beat Phelps, but the American famously took gold in a fingernail finish.

A quick finish from Phelps propels him from last place to first in the heats 50m of the men's 100m butterfly.

Their rivalry will resume once again in Friday night's final.

Catch up on the morning swimming session on our BBC interactive player here.

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