Four-time world champion Sebastian Vettel insisted Sunday that Red Bull could close the gap on run-away rivals Mercedes and mount a serious defence of their titles.
After finishing a fighting fourth in the Spanish Grand Prix behind winning Mercedes pairing of Lewis Hamilton and Nico Rosberg, and his own Red Bull team-mate Daniel Ricciardo, the German admitted his team face a scrap for more success.
Vettel, 26, started 15th on the grid after receiving a five-place penalty due to a changed gearbox, but carved his way through the field with a surging performance.
"It was fun," he said. "More fun than in the last race when we had to let people by. We were quite happy with the car in the race. We had to be patient.
"It's very tricky when you sit in a train - the car slides, the car in front of you slides, and you lose grip. Once the traffic was clear, we were able to use the pace.
"We had a good strategy and had two sets of softer tyres at the end and we could get past some people. I enjoyed it a lot and I think fourth is the best we could get today."
Vettel is fourth in the overall drivers' standing -- 55 points behind leader Hamilton -- with Red Bull trailing Mercedes in the constructors' standings by 113 points.
The German added that while Mercedes are currently out of reach, he has not given up on bridging the gap.
"They have a very good package with the engine, car and two very good drivers. All in all, that makes them so strong and difficult to beat."