Scuderia Toro Rosso technical director James Key left Sochi last weekend thoroughly disappointed by the team's lack of result.
Max Verstappen was enjoying a good top 10 run when his Ferrari power unit expired a little after the halfway mark, while team mate Carlos Sainz finished a distant 12th after incurring a time penalty for forcing Jolyon Palmer's Renault off the track.
"Max was in an easy sixth place, slightly shy of the Williams pace on the SuperSofts, a bit better on the Softs," Key explained.
"All he had to do was continue as he was doing, he was very competitive and maybe he could have challenged [Felipe] Massa towards the end as he seemed to have higher tyre degradation than us."
In addition to the penaly imposed upon him, Sainz' underperformance was also a case of bad luck.
"In a completely freak situation, Carlos picked up a piece of Red Bull front wing end plate in the front of his left hand sidepod.
"It was sticking out of the cooling inlet and dramatically increased engine temperatures and he had to turn his engine right down.
"It also lost him an awful lot of aero performance which meant he had both much reduced engine power and less downforce for the opening laps of the race.
"It was a huge opportunity missed, because from a car and driver perspective we did everything we could and had very bad luck with both cars."
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