$ mpc search title "when I was your man"
Bruno Mars/Unorthodox Jukebox/06 Bruno Mars - When I Was Your Man.mp3

$ mpc search title "when I was your man" | mpc play

play <position>
  Starts playing the song-number specified. If none is specified, plays number 1.

mpc clear; mpc search title "when I was your man" | mpc add; mpc play

title="your song title here"
mpc search title $title  | mpc add
mpc playlist -f '%position% %title%' | grep -i $title | head -n1 | cut - -d " " -f 1 | xargs mpc play

mpc clear
mpc search title "when I was your man" | mpc add
mpc play

mpc search title "when I was your man" | mpc insert
mpc next

mpc search title "when I was your man" | mpc add
mpc play $(mpc playlist | wc -l)

mpc searchplay filename "$(mpc search title 'when I was your man')"