Mercedes scored their best result of the year in Barcelona with a 2-3 finish.

Lewis Hamilton finished a comfortable second, while George Russell fended off a recovering Sergio Perez to claim his first podium of F1 2023.

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Horner was asked about the Mercedes resurgence after the race on Sunday.

He replied: “They were still 23 seconds behind at the end of the race. They’ve made a good step but I think we’ve got some stuff in the pipeline. 

“They’ve had a big upgrade. We’ve had some bits coming later into the season but look, for sure, a big step. 

“They’re a quality team and they’re going to be putting us under pressure in the second part of the year.”

It was Mercedes’ turn in Barcelona to be Red Bull’s nearest challenger as Ferrari and Aston Martin struggled.

Horner admitted that it’s difficult to predict who will be the second-fastest team in F1 given how it is changing on a race-by-race basis.

“Well the form is moving around,” Horner added. “If you look at Lando’s lap yesterday, the Mercedes look strong in the race today. The Ferraris didn’t have the pace we thought they might have. 

“The form behind us does seem to be moving around a lot at the moment. It’s difficult to predict who’s going to be at which event.”