The trio were out the front on their own for much of the final 20km and the BMC man made his move on Santa Caterina, the 16 per cent gradient final climb. But the effort taken to top the hill first, and drop Valverde, took its toll on Van Avermaet allowing Stybar to roll through the Siena streets to victory.
The Czech national champion's 2014 season was heavily disrupted by a crash at the Eneco Tour, which required him to undergo facial reconstruction surgery, and he missed the cyclo-cross season with a lingering shoulder injury.
But he showed he was back to full health with a perfectly executed and patient ride on the white roads of Tuscany.
As the race reached its final 30km a number of the strong favourites, including Fabian Cancellara, Peter Sagan, van Avermaet and Sep Vanmarcke, were part of a group of nine riders who enjoyed a slender lead over the peloton.
Van Avermaet's BMC teammate Daniel Oss made a solo effort off the front, which Vanmarcke followed soon after but the group came back together as Cancellara and co were unwilling to let the Belgian gain a lead.
The acceleration to bring back Vanmarcke saw Sagan and Cancellara dropped from the front group, and while the latter teamed up with Oss to try and bridge the gap, Sagan could not latch on.
>>> Watch: The best finishes at Strade Bianche (videos)
Then it was Van Avermaet's turn to attack, but as Stybar and Valverde worked to catch up, Vanmarcke ran out of gas and dropped back.
The trio stayed together as they passed through the city walls before the BMC rider made his move up Santa Caterina. Valverde cracked, but Stybar stuck to Van Avermaet's wheel and snuck past as the Belgian fell back.
Strade Bianche 2015
1. Zdenek Stybar (Etixx-Quick-Step)
2. Greg Van Avermaet (BMC) at 2 secs
3. Alejandro Valverde (Movistar) at 18 secs
4. Sep Vanmarcke (LottoNL-Jumbo) at 46 secs
5. Diego Rosa (Astana) at 56 secs
6. Oscar Gatto (Androni Giocattoli) at 59 secs
7. Rigoberto Uran (Etixx-Quick-Step)
8. Fabio Felline (Trek Factory Racing) at 1-02
9. Przemyslaw Niemiec (Lampre-Merida) at 1-03
10. Giampaolo Caruso (Team Katusha)
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Stuart Clarke is a News Associates trained journalist who has worked for the likes of the British Olympic Associate, British Rowing and the England and Wales Cricket Board, and of course Cycling Weekly. His work at Cycling Weekly has focused upon professional racing, following the World Tour races and its characters.
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