"Sagan is the best person who could have won the world title. He's a friend and always races well, so I'm happy he won. I was cheering for Italy of course but I think most people were happy to see Peter win," Nibali told Cyclingnews and La Gazzetta dello Sport during the Giro della Toscana.
"Everyone knows that Peter can win sprints and [especially] after a hard race. I recall a really tough stage at an edition of Tirreno-Adriatico and he even won that."
Nibali was amazed when reminded that Sagan also finished sixth at the 2013 world championships in Florence, when Nibali was fourth behind Rui Costa, Joaquim Rodriguez and Alejandro Valverde.
"Was he really sixth? It's true; he won the group sprint behind. Wow. Hopefully, we can make it too hard for him in Innsbruck…"
Nibali recalled the first time he met Sagan at a winter get together and remembered he was something special.
"We're rivals now and we so don't see each other as often as we did during our time together at Liquigas but we still look for each other at races and enjoy a laugh together and talk about our families," he said.
"I remember that the first time I met him was in the Dolomites at a winter get together in the snow. I like messing around on a mountain bike and was doing one-handed wheelies. I thought I was good and then Sagan started going hand-free wheelies in the snow. He could hardly speak a word of Italian or English but he showed what a great bike handler he is. He soon showed it in races too, winning a stage at Paris-Nice in 2010."
Nibali opted not to put himself up for possible selection for this year's world championships in Bergen because of bruised ribs he sustained in a crash on the Angliru stage of the Vuelta a España. He finished second overall in the race to Chris Froome and has spent the last two weeks recovering from his second Grand Tour of the season.
Nibali finished fourth on stage 1 of the Giro della Toscana on Tuesday, testing his form by forcing a breakaway on the final climb of the stage. He opted not to race the Coppa Sabatini on Thursday to be fresh for Saturday's Giro dell'Emilia, which finishes with the climb to San Luca above Bologna. He will also ride the Tre Valli Varesine on Tuesday before recovering for the following Saturday's Il Lombardia.
Ending 2017 at Il Lombardia
Nibali won Il Lombardia in 2015, the last time the final monument Classic of the season finished along the edge of Lake Como. He is keen to add another win to his palmares. It could also be his 50th career victory.
"I've recovered after the Vuelta and now we're close to Il Lombardia, so I've got to take advantage of my form and the hard work we did at the Vuelta to end the season on a high," he pointed out.
"I've always liked Il Lombardia, it's a hard race. I've already checked out this year's course. I know the roads, too. We'll see what happens, there are a lot more riders who are on form and can win Il Lombardia this year, including Sergio Henao, Julian Alaphilippe, Gianni Moscon and others. I feel good and want to be up there."
Il Lombardia will be Nibali's last race of 2018 after more than 80 days of racing since the Vuelta Ciclista a la Provincia de San Juan in Argentina in late January.
Tour de France in 2018?
"I've still got to finish 2017 before I can start thinking about 2018," he said with a laugh.
"The Worlds in Innsbruck look like they suit me, and it should be a hard race but they're still a full year away. I need to be on form then, secure a place in the Italian team and ride well.
"I want to see the full route of the Giro d'Italia and the Tour de France before making a decision on my big goals for 2018. We've seen that the Giro will start in Israel but we don't know much about the Tour yet. I want to wait to see what comes out, including that of the Vuelta, because it could be the best way to prepare for the World Championships."