Nottingham Forest stunned Manchester City 3-1 at the City Ground on Saturday, as Liam Delap scored twice against his former club and the champions slumped to a third consecutive Premier League defeat. The result left City six points behind leaders Arsenal, who ground out a 1-0 win over Hull City earlier in the day, and turned what had looked like a procession at the top of the table into a genuine title race.

Forest struck early and never let go of the game. Jair Cunha caught City defender Josko Gvardiol in possession in the sixth minute, surged forward and slid the ball into the bottom left corner to give the home side a lead that electrified a ground which had not seen its team score at home all season. Before twenty minutes had passed, Delap had doubled the advantage, punishing more slack defending to make it 2-0.

City, who had opened the campaign with seven straight league victories, looked rattled rather than ruthless. Their passing was hurried, their defending uncertain, and Forest, who began the day 19th in the table with a single point from their previous five matches, played with a freedom that belied their position. Rayan Cherki gave the visitors hope early in the second half, halving the deficit with a fine strike, but Forest weathered the pressure that followed.

The decisive moment came in the 74th minute. With City pushing forward in search of an equaliser, Delap broke away on a rapid counterattack and smashed a shot in off the inside of the far post for his second goal of the afternoon. The City Ground erupted, and Forest head coach Oliver Glasner sprinted half the length of the field to celebrate with his players. "One of my best running stats, I guess," he joked afterwards.

For Delap, the afternoon carried an extra edge. A product of City's academy, he was facing the club that developed him, and his two goals did more damage to their title defence than any opponent has managed all season. His second, a composed finish at full sprint, was the kind of goal that explains why Forest paid a reported £50 million for him, and why City may come to regret letting him go.

For City, the defeat confirmed a slide that is becoming hard to dismiss. Three straight league defeats, after seven straight wins, is the worst run of the season for the champions, and the manner of them is the concern: goals conceded through basic errors, leads surrendered, and a defence that no longer looks impregnable. Head coach Enzo Maresca insisted there was no reason to panic. "We are conceding too many goals unfortunately and we need to improve that," he told the BBC, urging calm before the international break.

Arsenal, meanwhile, did what champions do. Their 1-0 win over Hull was neither fluent nor convincing, but it was effective. Hull stayed organised and frustrated the league leaders for more than an hour before captain Martin Ødegaard found a way through in the 72nd minute. It was Arsenal's sixth league win by a single-goal margin this season, and it took them to 27 points from ten games, six clear of City at the summit.

The result also reshaped the bottom of the table. Forest's victory, only their second of the league season, lifted them two points clear of the relegation zone, and it pushed neighbours Manchester United into the bottom three ahead of their Sunday match against Aston Villa. For a club that had yet to score a home goal before Saturday, it was a transformation in a single afternoon.

Elsewhere on Saturday, Leeds United edged Tottenham Hotspur 1-0, with substitute Noah Okafor scoring in the 79th minute, just 97 seconds after coming on, to end a two-month winless run. Newcastle United drew 1-1 at Fulham. The results added to a weekend that delivered shocks at both ends of the table.

City now head into the international break with questions to answer and a six-point gap to close. Their next league fixtures will show whether this is a brief stumble or the moment their grip on the title began to loosen. Arsenal, for their part, have the cushion and the momentum, and a habit of winning tight games that has carried them to the top. Forest, suddenly, have belief, a home crowd behind them, and proof that on their day they can beat anyone.