Harmonically, this 1979 tune is such a feast that after several decades of casually listening to it, I never caught on that it actually modulates too. In fact, multiple times: on the way out of the pre-chorus and into the chorus (first heard at 1:17) and then back to the original key (first heard at 1:50), then a second time.
Co-written by Michael McDonald and Kenny Loggins, the track hit #1 in the US — one of only a handful of non-disco releases to do so in the first half of 1979.