Up all night I could not sleep
The whiskey that I drank was cheap
With shakin' hands I went and I lit up my last cigarette
Well the sun came, night had fled
And sleepy eyed I reached my bed
I saw you sleepy dreamin' there all covered and warm [ Lyrics from: http://www.lyricsmode.com/lyrics/d/doobie_brothers/south_city_midnight_lady.html ]
South city midnight lady
I'm much obliged indeed
You sure have saved this man whose soul was in need
I thought there was no reason
For all these things I do
But the smile that sent out returned with you
When day has left the night behind
And shadows roll across my mind
I sometimes find myself alone out walkin' the street
Yes, and when I'm feelin' down and blue
Then all I do is think of you
And all my foolish problems seem to fade away
South city midnight lady
I'm much obliged indeed
You sure have saved this man whose soul was in need
I thought there was no reason
For all these things I do
But the smile that sent out returned with you
I believe this song is about a one night stand, and remembering the event with warm feelings. This was the pre-hiv 70's casual sex was commonplace, and the possible consequences were minor compared to nowadays. I think the last line in the chorus is actually: "but the smile that (i) sent out returned with you". Which makes more sense and fits the one night stand scenario.