MELBOURNE (Reuters) - Red Bull team principal Christian Horner hailed an "extremely encouraging" Friday for the Formula One champions at the season-opening Australian Grand Prix after they banished some winter testing demons with a strong showing in practice.
Red Bull's pre-season was abysmal, with neither quadruple champion Sebastian Vettel nor team mate Daniel Ricciardo able to complete a race simulation due to reliability problems, but the pair clocked up ample mileage on a sunny day at Albert Park.
Vettel completed 51 laps and finished fourth on the time-sheets in the second practice session, only 0.756 seconds adrift of Mercedes' pace-setting Lewis Hamilton.
His new Australian team mate Ricciardo lapped the Albert Park circuit 64 times for the day and finished sixth fastest in the second session.
"I think Sebastian today has covered a third of the mileage of his total winter," Horner told reporters.
"Obviously Daniel has done pretty much a race distance today so that's extremely encouraging for our guys and the guys back in Paris at Renault.
"Hopefully it bodes well on the weekend. The most important thing is to see the chequered flag on Sunday, and that, in itself, is an enormous challenge."
All of the teams have struggled to come to terms with the new turbocharged hybrid engines, but Red Bull's preparations were particularly blighted by their troubled Renault power unit.
Friday was not all smooth sailing, with Vettel forced to return to pit with a heat problem during the first practice.
The 26-year-old German, bidding for a 10th straight race win on Sunday, also took a skid onto the grass in the second session, one of a number of drivers that struggled with the new V6 engines increased torque and reduced downforce.
Horner was under no illusions that the team still faced a battle to catch up.
"We still have an awful lot of work to do," he said.
"We can still see that there's quite a gap to certainly Mercedes and Ferrari but we're starting to realise what that gap is. By the end of this weekend, we should hope to have a bit more clarity.
"But the way the team has responded to the challenge has been fantastic. There's a real desire and inner strength within the team.
"This is where we'd have dearly liked to have been at the first test but that wasn't the case and we've got some ground to make up."
Editing by Alan Baldwin