Defeat at Old Trafford on Sunday gave Australia a 2-1 lead in the series and ensured they retain the Ashes in England for the first time since 2001.
He has scored 110 runs in eight innings with a top score of 31 at Old Trafford when he dropped down the order.
The former captain, top of the worldwide rankings, has carried his team's batting with three centuries and two fifties, including a double-century in the win in Manchester, with Marnus Labuschagne the only other batsman who has shown any consistency.
"Little things like that no-ball (that cost Jack Leach the wicket of Smith in Manchester) could have made a big difference but you can't look at ifs and buts, you got to look forward at this next Test".
The immediate threats in front of England are the number one Test bowler and batsman in the Australian ranks, with Pat Cummins and Steve Smith raising the bar in terms of what constitutes individual dominance in a series. "I've never seen batting like that".
"We came here to win the Ashes not just retain them".
England captain Joe Root says he wants to carry on as skipper despite losing the Ashes series to Australia. But Bayliss has put those questions to rest, saying, "He's not come under question from anyone making any decisions". "He's under no pressure at all".
Curran, who hasn't played any of the Tests so far despite his promises as a young all-rounder, has been roped in to boost both the batting and bowling.
"I know the direction I want to take this team", Root said.
England talisman Ben Stokes was included in an unchanged 13-man squad but will be assessed to find out whether he is fit to bowl at the Oval.
The South African-born Roy struggled to convert a solid run of form in ODI cricket to success at Test match level.
In the continuing absence of the injured James Anderson, Root will be relying on his new-ball pairing of Stuart Broad and Archer to do the damage.
Marsh (match figures of 5 for 86) and Peter Siddle (6 for 67) were Australia's two leading bowlers at The Oval when Australia won the final match of the 2015 series, standing up the seam of the Dukes ball and moving it around after the series had been decided in England's favour at Edgbaston and Trent Bridge.