[4] The key move of the race was made on the Oude Kwaremont by Geraint Thomas (Team Sky), Zdeněk Štybar (Etixx–Quick-Step) and Sagan.

With approximately 4 kilometres (2.5 miles) remaining, Thomas attacked and was able to take a solo victory, and became the first British rider to win the race.

Sep Vanmarcke (LottoNL–Jumbo) slipped on the Paterberg, though this resulted in nothing worse than a broken shoe; however, a major crash early in the race caused significant problems for a number of riders.

The worst affected was Fabian Cancellara (Trek Factory Racing), one of the major favourites for victory; he broke two vertebrae, ruling him out of the remainder of the classics season.

This was a reference to Peter Sagan's actions after the 2013 Tour of Flanders, when he pinched the bottom of Maja Leye during the podium ceremony after the race.

Initially, the route headed north, but after a short distance it turned south-east to reach the town of Avelgem after 12.8 kilometres (8.0 miles).

The race then entered a long loop without any significant climbs, though it did include the Paddestraat, another flat section of cobbles.

In past editions of the race this was the section where a decisive breakaway was formed; the combination of the two climbs was also a major feature of the Tour of Flanders.

The route continued south to the penultimate climb of the day, the Karnemelkbeekstraat, with 29.7 kilometres (18.5 miles) remaining, then turned north-west for the final part of the race.

[4] The winner of the 2014 E3 Harelbeke, Peter Sagan (Tinkoff–Saxo) was one of the major pre-race favourites, although his early-season form had been mixed and he had won just one race in 2015 to that point.

However, one of his most important teammates, Stijn Devolder, crashed in Dwars door Vlaanderen earlier in the week, potentially affecting Cancellara's chances.

[4][11] Nairo Quintana (Movistar Team) also entered the race as he had in Dwars door Vlaanderen; he was preparing for cobbled stages at the Tour de France rather than competing for the win.

A large number of riders crashed, including Fabian Cancellara (Trek Factory Racing), Sebastian Langeveld (Cannondale–Garmin), Robert Wagner (LottoNL–Jumbo), Lars Boom (Astana) and John Degenkolb (Team Giant–Alpecin).

[16] Shortly afterwards, the peloton climbed the Taaienberg, where Daniel Oss (BMC Racing Team), Matteo Trentin (Etixx–Quick-Step) and Matti Breschel (Tinkoff–Saxo) attacked and were soon joined by Tiesj Benoot (Lotto–Soudal).

[14] Tinkoff–Saxo, along with Team Sky, took up the chase in earnest and reduced the breakaway's lead to under two and a half minutes with 67 kilometres (42 miles) left.

He slipped in the mud and had to put a foot down on the cobblestones; this damaged his shoe and left him unable to clip into his pedal, reducing his ability to apply power on the climbs.

[16] At the top, with 17 kilometres (11 miles) left, Oss was leading the group, while Greg Van Avermaet, BMC's team leader, was a couple of places further back.

Van Avermaet was riding on the wheel of Alexandr Kolobnev (Team Katusha), who missed a corner and was forced to brake.

Van Avermaet also braked; this action caused him to somersault over his handlebars and crash, injuring him and taking him out of contention for the rest of the race.

With 4 kilometres (2.5 miles) left, Thomas attacked the lead group and Štybar waited for Sagan to respond.