Mercedes boss Toto Wolff said Valtteri Bottas and Lewis Hamilton "seemed to open the sea" for Max Verstappen to lead into Turn 1 of the Mexican Grand Prix.
Verstappen had a brilliant getaway in Mexico City and got alongside Bottas and Hamilton heading down to Turn 1. With Bottas braking and giving Verstappen space, the championship leader was able to pass both black cars around the outside.
Bottas was then spun out of contention when he got hit by Ricciardo behind. Verstappen was in control from that moment on, extending his lead over Hamilton in the process.
Asked about that moment after the race, Wolff told Sky Sports: "Yeah that should not happen.
"I think we had two cars in front and we seemed to open up the sea for Max to come around the outside. Even so, the spin afterwards and the complete loss of points with Valtteri's car when it could have been a third or fourth place is annoying to say the least."
Despite his frustrations, Wolff felt Red Bull's outright pace was too strong on the day for Mercedes to win.
"You have to congratulate Red Bull because the pace was just on another level. I don't think we could have won the race even if we would have stayed ahead in the first corner because they could have driven circles around us around the pit stops. In the end, for Lewis' championship, it was damage limitation, as for the constructors', Valtteri spinning out at Turn 1 was just very painful."
Horner and Red Bull had been upset at seeing Mercedes lock out the front row in qualifying on Saturday. Horner admitted that outcome probably helped Verstappen take control of the grand prix straight away as he used the run down to Turn 1 to lead the race.
"I think as it transpired being on the second row was actually probably the best place to be starting this race.
"I thought Valtteri was fair into Turn 1. He allowed Max enough space, which is the rule down to Turn 1. Max made best use of it, braked incredibly late. Almost took a standard racing line into there and was able to take the lead.
"We were just fortunate with Checo [Perez] he was able to avoid the accident between Daniel and Valtteri. I thought it was a good start, we made the tow work and Valtteri played fair."