England were "too casual" on day one of the second Ashes Test and must realise the contest "is not just another game", says former captain Michael Vaughan.
Amid a lacklustre England display, Australia reached 339-5 at the close having been put in to bat at Lord's.
The hosts dropped two catches, bowled 12 no-balls and lacked consistency with the ball and now have an uphill task as they bid to level the series.
"I worry about England," Vaughan said. "I see too much casualness."
He added: "They switched off last week at Edgbaston and today when it has really mattered, England haven't been switched on quick enough and hard enough to win the moment.
"It has cost them."
England have been widely praised for their resurgence under coach Brendon McCullum and captain Ben Stokes after an attacking approach on the field, coupled with a more relaxed environment off it, helped them win 11 of their first 13 Tests.
But they were beaten by two wickets in a dramatic first Test at Edgbaston last week, after which opener Zak Crawley said the Lord's pitch would suit England better and they would "win by 150 runs".
"Some of the messages, particularly after the loss at Edgbaston, were very positive, almost as if England had won that Test match. They hadn't, they'd lost," Vaughan said.
"If you are going to talk the talk, you have to walk the walk."
He added: "I just get the sense that it's just another game of cricket. The Ashes is not just another game of cricket.
"You can be as casual as you like against many other sides, but I'm afraid this is when it matters. Against Australia, this is what defines you."
'Absolutely shambolic'
England dropped both Australia openers in the morning session - first slip Joe Root unable to take a tough, low catch after an edge by Usman Khawaja and Ollie Pope spilling a more straightforward chance off David Warner at fourth slip.
They also seemed surprisingly flat, summed up by Australia's batters having to wait for the hosts to emerge after a rain delay in the gloom.
Former England batter Kevin Pietersen described the situation as "absolutely shambolic".
"It is one thing swanning around saying 'this is a wonderful team to play in', 'we are creating the best environment'," Pietersen told Sky Sports.
"The England bowlers should have been on the stairs saying 'we want to bowl at Australia'. It is all too easy and nice."
After Australia eased to 73-0, Josh Tongue, the pick of England's bowlers in his second Test, bowled Khawaja and Warner either side of lunch to bring England back into the game.
But Steve Smith hit 85 not out, sharing a stand of 102 with Marnus Labuschagne and 118 in 20.2 overs with Travis Head.
Head capitalised on tame and wayward England bowling to strike 77 from 73 balls before becoming the first of two wickets in a Joe Root over late on.
"They haven't bowled well enough, haven't caught well enough and they're bowling no-balls," Vaughan said. "It is just not good enough.
"When they got David Warner out, Steve Smith got four or five juicy half-volleys. It got him going.
"They got the key wicket of Labuschagne and Travis Head got two gifts.
"The match sharpness of this England side over the last two Test matches has just not been there."
