Venue: Sydney Cricket Ground Date: Saturday, 16 July Kick-off: 10:55 BST |
Coverage: Live commentary on BBC Radio 5 Live and live text commentary on BBC Sport website and app. |
Chessum will make his England debut in the deciding game against Australia.
Chessum will replace Itoje in the second row.
The number seven will be worn by Lewis Ludlam.
Danny Care will start at scrum-half in the one change to the backline.
After the 30-28 defeat in the opening game, Care was dropped and Poortvliet made his England debut.
"We've had a squad of 36 who have competed hard and we're really proud of them," said Jones.
There is a strong squad of 23. The group has developed well throughout the series.
The goal is to win the series and a historic Test match at the Cricket Ground.
Jack is one of the replacements after recovering from a rib injury.
Itoje and Underhill both sustained concussions after starting in the second Test, while team-mate Tom Curry had already left the country.
Australia's Jordan Petaia and Allan Alaalatoa are not in the series because of concussions.
The Australian team is: Hodge, Wright, Paisami, Kerevi, Koroibete, Lolesio, White, Valetini, Hooper, Wilson, Philip and Tupou.
Replacements : Bell, Ala'alatoa, Ikitau, Vunivalu.
Hill, Chessum, Stuart, George, Genge are England's players.
REPLACEMENTS : Heyes, Isiekwe, Van Poortvliet, Joseph, and Arundell.