The substitute returned from injury with a bang as he condemned Pep Guardiola to a fourth successive defeat in all competitions for the first time in his managerial career.

Erling Haaland had given City a deserved lead in the first half, but it was pegged back by another substitute in Joao Pedro in the 78th minute.

O'Riley then piled the misery on their visitors with a composed finish five minutes later, ensuring Fabian Hurzeler's side, which was on the wrong end of a comeback against Liverpool last time out, came out on top.

It was a win that lifted Brighton to fourth on the table, while second-placed City missed the chance to go top, sitting two points behind Liverpool before it played against Aston Villa later in the day.

City is so used to writing history given its successes in recent years, but it is making headlines for the wrong reasons this time around.

Aside from Guardiola losing four straight games for the first time, it is also the first time City has suffered four consecutive defeats since August 2006.

Guardiola conceded City needs to "change things quickly" and suggested his team, which has been rocked by injuries, is simply finding matters too tough.

"We are not able to do 90 minutes right now," Guardiola said. "We played a really good first half and moments in the second half.

"We lost again, so clean our heads, international break and hopefully our players come back fit.

"We have to try and win games again. We were not able to sustain the rhythm in the second half. Four [defeats] in a row. We have to change things quickly.

"The schedule becomes tough, but it is going to happen when the players come back. Maybe after seven years, winning six Premier Leagues, maybe one year another team deserve it. We'll see."

City has conceded 10 goals during this losing streak, managing just four goals of its own in that time.

The reigning Premier League champion has more tough games coming up, with Tottenham Hotspur and leader Liverpool the next opponents in the top flight

Take nothing away from Brighton, though. It is now unbeaten across its first six Premier League home games of the season, its best such start to a top-flight campaign since 1982-1983 when it went seven home games without defeat.

Despite all the success, Brighton manager Hurzeler wants his side to stay humble.

"Last week, we talked about a great performance but not the result against Liverpool. Today we got a result, so I'm happy," Hurzeler said.

"On the one hand, it's important to gain self-confidence from games like this. On the other, it's important to stay humble, keep focusing on the hard work and keep focusing on the process."

With his side trailing at half-time, there was plenty of work for Brighton to do, but Hurzeler kept his instructions to his players simple.

"In possession, to stay more patient and to make City move. In the first half, we played too many vertical balls and gave too many easy balls away. The subs were great for us. They had an impact and if you have that in the squad, it helps you," he added.

Match winner O'Riley became the first player to score against City on his Premier League debut since Steven Bergwijn for Tottenham Hotspur in February 2020.

"Part of it is how he [O'Riley] worked for his comeback. A lot of players would keep their head down and be negative, but he was very positive. I'm happy he got what he deserved," Hurzeler said.

Hurzeler's emotions were echoed by Brighton forward Joao Pedro, who also scored after coming off the bench.

"First, I'm happy to be back. I know I'm an important player for the team, so when we win like this against a big team it is good. Now we have time to breathe and win more games," he said.

"I'm happy to score. After two months out, I'm very happy to be back.

"Last season we dropped too many points and the gaffer told us to believe in ourselves this season, and we are doing well this season against the big teams."