Daniel Ricciardo admitted he was surprised by the competitiveness of his Red Bull Racing team in practice for the Mexican Grand Prix.
The Australian, however, has ruled out fighting Mercedes for pole position tomorrow.
Teammate Daniil Kvyat was second quickest in FP2, just over two tenths of a second behind the pace-setting Mercedes of Nico Rosberg.
Ricciardo was third fastest in one of Red Bull's most promising showings of the season so far.
He said he did not expect his team to be so fast, although he conceded the layout of the track was helping its cause.
"Pretty much all the corners on the track suit us," said Ricciardo. "It's the one straight where we lose all our advantage, but all these sort of tight, twisty corners and the fast flowing Esses in the middle work to our advantage.
"I think we are a little bit more competitive today than we thought we would be, but we'll see what happens tomorrow."
Pole "not realistic"
When asked if pole position was within reach, he said: "Not realistic. We can hope, but I think if we were to stay where we are, within a few tenths of Mercedes, we'd be really happy with that."
Ricciardo believes the altitude was affecting the feeling of his brakes, making things trickier during the first hours of running at the Autodromo Hermanos Rodriguez.
"I personally had a few issues with braking. I wasn't quite comfortable," he said.
"I don't know how much the altitude is affecting that, but I know you lose a lot of downforce and when you don't have the downforce under braking the car slides a lot more, so maybe that's part of the feeling as well."
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