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He will play against his former Canterbury-Bankstown club at Mount Smart Stadium on Saturday.
The 21-year-old started at standoff in each of the club's NRL trial wins over Melbourne and the Wests Tigers.
Head coach Stephen Kearney has given him the chance against a club he played for in the former Intrust Super Premiership (now the Canterbury Cup NSW) in 2017 before switching to Penrith last year.
While Keighran will be the only player on first-grade debut for the Warriors on Saturday, another former Bulldog Lachlan Burr will start at loose forward in his first outing for the club and his first NRL appearance in three years after last playing for Gold Coast in 2016.
Keighran becomes Warrior number 231 and Burr number 232, with Burr coming into the side for Isaiah Papali'i who has been stood down for a week for a breach of club standards.
After two games in 2009, he went on to play 177 games for North Queensland and St George Illawarra before being lured home to rejoin his original club.
Ah Mau was a stellar performer for the Dragons last year while Keighran and Burr both excelled in the ISP. Keighran was named in the centres in the ISP team of the year with Burr recognised as the Bulldogs' ISP player of the year.
Also returning to the NRL is hooker Nathaniel Roache, who will make his first appearance since 2017. Veteran Issac Luke, who has been recovering from shoulder surgery, hasn't been included.
In other selection decisions Warriors head coach Stephen Kearney has given different roles to last year's regular centres Peta Hiku and Solomone Kata. Hiku is set to line up on the left edge combining with second rower Tohu Harris and wing Ken Maumalo while the right edge combination sees Kata linked with David Fusitu'a and second rower Adam Blair.
With Dally M interchange player of the year Jazz Tevaga confirmed in his familiar No.14 jersey, Ah Mau and Sam Lisone are named as the bench props with Bunty Afoa handed a starting spot. In jersey No.17 is Blake Ayshford, covering the outside backs and the back row. Also on the extended eight-man bench is Chanael Harris-Tavita, who was competing for the standoff position.
Warriors team to face the Bulldogs - Saturday, 5pm, Mt Smart Stadium:
1 Roger Tuivasa-Sheck (c)
2 David Fusitua
3 Peta Hiku
4 Solomone Kata
5 Ken Maumalo
6 Adam Keighran
7 Blake Green
8 Agnatius Paasi
9 Nathaniel Roache
10 Bunty Afoa
11 Adam Blair
12 Tohu Harris
13 Lachlan Burr
14 Jazz Tevaga
15 Sam Lisone
16 Leeson Ah Mau
17 Blake Ayshford
18 Gerard Beale
20 Ligi Sao
21 Karl Lawton
22 Chanel Harris-Tavita