A second-string Nottingham Forest served up the shock of the Premier League weekend as they ran through an insipid Chelsea side in west London to keep their dual bid for Premier League safety and European glory alive.

After Vítor Pereira announced eight changes from the team that beat Aston Villa in the Europa League semi-final first leg on Thursday night, and with the second leg just three days away, the Forest boss said he had “changed the players but not the spirit” of his team. If there were eyebrows raised when the news came in, Pereira’s appraisal turned out to be entirely correct. His understudies – led by the two-goal Taiwo Awoniyi and the winger Dilane Bakwa – were every inch the match of the many amortised investments that lined up for their opponents.

It was a disastrous first half for Chelsea in a number of ways. They were behind from the second minute after Bakwa caught Marc Cucurella on his heels, peeled away on the right and dug out a cross to the back post which Awoniyi headed home. By the 15th minute the lead had doubled and from precisely the same route: this time Bakwa simply dribbled past Cucurella before crossing and Awoniyi went for the ball again, only to fall to the ground after Malo Gusto had been tugging on his shirt. After the video assistant referee recommended a review, a penalty was given and Igor Jesus finished coolly.

Hardly the ideal start in front of a Stamford Bridge crowd on the verge of mutiny, and now a 13th Premier League game in a row without a clean sheet. But Chelsea’s performance did not kick on from there, rather it stayed stuck in neutral. They were sluggish across the piece, apparently short on attacking ideas and consistently bested in duels by their opponents. Pereira’s changes had seemed bold before kick-off, but no more.

Calum McFarlane, Chelsea’s interim head coach, looked largely impotent on the sidelines meanwhile, and also had to deal with a serious injury to the debutant Jesse Shaun Derry. Derry had been a surprise inclusion by McFarlane, and he had struggled in the match.

As the half approached added time a Chelsea corner went through to the 18-year-old winger whose first header was loose. He attacked the second bravely and won it, but was immediately clattered by fellow teenager Zach Abbott in a head-to-head collision. Both men were ultimately substituted, but while Abbott walked off, Derry left the field on a stretcher. Anthony Taylor awarded a penalty for Abbott’s challenge but – after a break in play of more than 10 minutes – Cole Palmer was unable to convert, Matz Sels diving low to his right to save well.

Pereira was able to bring on three of his rested stars at half-time and almost immediately those changes decided the game. Within five minutes of the restart one reinforcement, Elliot Anderson, had split the lines with a pass to send another, Morgan Gibbs-White, to run clear beyond Cucurella again. The Forest No 10 – in such fine form in recent weeks – laid the ball on a plate for Awoniyi.

The cameo from Gibbs-White was brief. In the 60th minute he and Robert Sánchez were involved in another clash of heads, this time as the pair tried to chase down a loose ball. With a bandage around his head and what looked like a lot of blood underneath, Gibbs-White was withdrawn for Chris Wood after another lengthy stoppage, while Sánchez departed for Filip Jörgensen, meaning a league maximum of four concussion substitutes had been used in the game.

With just over a quarter of an hour remaining Chelsea had the ball in the back of the net, João Pedro heading home after seeing his first effort saved by Sels, only for VAR to overturn. Into added time, however, and the Brazilian scored again, taking a Cucurella delivery on his chest and smashing an overhead kick into the net. This time there was no intervention from VAR, but as Chelsea recorded their first Premier League goal in seven games, there wasn’t much in the way of cheering either.