By Alan Baldwin
(Reuters) -Seven-times Formula One world champion Lewis Hamilton found some much-needed pace on Friday as Mercedes responded to the threat of a fifth successive Red Bull win by leading Austrian Grand Prix practice.
Max Verstappen, Red Bull's championship leader, had been quickest in the opening session with a time of one minute 05.143 seconds around the Red Bull Ring where he won last Sunday's Styrian Grand Prix.
Hamilton then clocked a lap of 1:04.523 in the afternoon, when he also slid into the gravel, with team mate Valtteri Bottas 0.189 slower and Verstappen third.
The Briton remained wary of the Red Bull threat, however.
"They've definitely got something extra in their bag, I already know that," he said.
"But I think we've made some small progress today. I think they still have the two tenths or maybe it's a tenth and a half. We've definitely made some small steps forward but not enough.
"I just expect them to turn up (the engine) a little bit more tomorrow," he added. "But we'll be pushing, trying to make that gap as small as possible."
Verstappen will be chasing his third win in a row, and fifth of the season, with plenty of his Dutch fans cheering him on in the biggest crowd of a season restricted by COVID-19 precautions.
The 23-year-old is 18 points ahead of Hamilton after eight races. Red Bull have won four races in a row, the first time they have done that since 2013, when they were last champions.
"I felt good in the car," said Verstappen.
"We just need to make sure we have a bit more pace on the soft (tyre) because on the medium we look good and also on the long runs we look decent.
"I think it will be tight. They (Mercedes) definitely have improved a bit," he added.
The two Mercedes-powered Aston Martins of Lance Stroll and Sebastian Vettel were fourth and fifth in the second practice with Red Bull-owned AlphaTauri sixth and seventh with Yuki Tsunoda and Pierre Gasly.
Fernando Alonso ended the day eighth for Alpine, ahead of McLaren's Lando Norris, who spun.
Teams were also testing a new Pirelli tyre with a stronger construction, after high-speed failures in the Azerbaijan Grand Prix on June 6. It could be introduced at this month's British Grand Prix if approved.
Pirelli have also brought softer compounds for this weekend, which should mix up the strategy, and temperatures should be cooler.
Verstappen's Mexican team mate Sergio Perez, winner in Azerbaijan, ended the day 11th fastest.
Ferrari's Charles Leclerc and Carlos Sainz were second and third in the opening session but the Monegasque was 16th and the Spaniard 13th after lunch.
Several names more familiar to Formula Two fans also appeared on the morning timing screens, with Chinese test driver Guanyu Zhou making his first Friday appearance in Fernando Alonso's Alpine.
Israeli Roy Nissany took George Russell's Williams for the session, and Britain's Callum Ilott took a turn in Antonio Giovinazzi's Alfa Romeo.
Formula Two leader Zhou was the quickest of the stand-ins, with the 14th-best time.
(Reporting by Alan Baldwin in London, Editing by Hugh Lawson, Timothy Heritage and Andrew Cawthorne)