Mendes hit the stage, guitar in hand, to help JT with "What Goes Around...Comes Around," slowing down the already-downtempo song for an especially dramatic, gospel-like take on the FutureSex/LoveSounds single. The "In My Blood" singer took over the second verse, perfectly matching Timberlake's pleading vocals.
The duo ended the song with a line from Timberlake's Chris Stapleton collaboration "Say Something," and as Mendes exited the stage, the band picked up with the Man of the Woods standout.
Timberlake performed a full set to open day 2 at Las Vegas' T-Mobile Arena, kicking things off with the pumping beat of "Filthy" and leaving the crowd dancing with "Can't Stop the Feeling!," and a pack of hits in between. Find his full set list below:
LoveStoned/I Think She Knows
Man of the Woods
Cry Me a River
What Goes Around...Comes Around (with Shawn Mendes)
Can't Stop the Feeling!
iHeartRadio Music Festival day 2 continues with a full set from Mendes, plus fellow performers Kelly Clarkson and Imagine Dragons.