The 27-year-old Brazilian joined Barcelona from Liverpool in January 2018 for an initial 120 million euros in a deal that included another 40 million euros in potential add-ons.
Labuschagne was not confirmed as playing until Sunday morning when Australia star Steve Smith was ruled out with concussion, having been hit by a Jofra Archer bouncer during his 92 on Saturday.
Pozzovivo was involved in the collision while training near Cosenza in southern Italy.
The champion pair retired after the 2016 Olympic Games, where Eaton won decathlon gold and Theisen-Eaton took the heptathlon bronze medal.
Yamaha's Fabio Quartararo completed the podium and Australian Jack Miller was one of four riders who fell during the race.
Medvedev's upset win sent him into a title showdown with another unexpected finalist, 16th-seeded Belgian David Goffin, who defeated France's Richard Gasquet 6-3, 6-4 to reach his first ATP Masters 1000 final.