OK, I just did a little experiment on searching. If you put the one line lyric down and then put song chords it seems to come up with the right song for me and the chords. I think the lyric has to be fairly specific and the more well known the part of the lyric, the better chance of coming up with the right song. Anyway, try putting the lyric you know followed by "song chords". It may only work sometimes, but it worked for me on two songs I tried.
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