England fast bowler Jofra Archer has the "X-factor" that unsettles opposition batting lineups, said former Australia captain Steve Waugh who believes the evenly-balanced Ashes series would be decided by a few key moments.
Archer made his test debut in the drawn second match at Lord's and produced several spells of menacing quick bowling, hurrying the Australian batsmen up and forcing them into evasive action from deliveries that averaged more than 145kph.
He was also involved in the test's major talking point when Steve Smith was felled following a sickening blow in the neck from an Archer bouncer.
He also hit Marnus Labuschagne, who replaced Smith on the fifth day and became the first concussion substitute in test cricket, in the face grill of his helmet.
"It gives you the X-factor, knowing that you have that sort of bowler in your lineup when you can intimidate the opposition," Waugh told a Cricket Australia podcast.
"You can make things happen on a flat pitch and potentially get wickets in clumps.
"He's a real asset to England."
Waugh did not find any problems with Archer's stamina either after the Barbados-born 24-year-old bowled 44 overs and took 5-91 at Lord's.
"If he plays four test matches in a row that will test him out," Waugh said.
"So far he's come through with flying colours. (He bowled) 40 overs and each one was as quick as the previous one.
"He had an impressive debut but test cricket is about longevity and how you back up and how you handle conditions. But from England's point of view, so far so good."
Waugh, who stared down some of the fastest bowlers in the world like Malcolm Marshall and Shoaib Akhtar in a career that netted more than 10,000 test runs, said that Archer had one of the more economical bowling actions he had seen.
"I can't say I have ever seen anyone bowl like that," he said. "He ambles in, gets very close to the crease, makes the most of his height.
"He has got a very simple action and in a lot of ways a similar action to (Australian fast bowler) Glenn McGrath in that it's very repeatable. I can't see too much going wrong with it.
"His control is very good for that reason. He has that deceptive pace and has a wicked bouncer so that is something our team will have to analyse and work out to play him."
While Australia had won the first test at Edgbaston by 251 runs, the way England fought back in the second test at Lord's indicated how close the Ashes series would be.
"It really depends on who wins the big moments," Waugh said.
"It will come down to who is consistent. I think we can win the series and England will probably say they think they can.
"It will make for a great last three test matches."
The third test starts at Headingley in Leeds on Thursday.