Sunderland boss Steve Bruce feels defeat at Stoke City in February sparked their slide.
Bruce's men would lose six and draw one of their next seven games, including tough tests against the likes of Tottenham Hotspur, Manchester City and Liverpool, before ending the campaign with three wins in five outings.
"That game [Stoke] was the biggest turning point of the season for me," Bruce told safc.com.
"We were 2-1 up with a few minutes to play having played really, really well.
"That day was instrumental [in the downturn]. We got ourselves in a wonderful position and unfortunately didn't manage to see it through.
"That, with the two or three defeats around that time against your Chelseas, Tottenhams and Evertons, chipped away at the little bit of confidence we had.
"Slowly but surely the injuries took hold and it's been a catalogue since then."
