The 19-year-old left-handed batsman became the first debutant in Test history to register a half century. He came agonisingly close to world record century but fell short by 2 runs. Agar was the top scorer in Australia's first innings which ended at 280 in 64.5 overs.
Agar made a 101-ball 98 with 12 fours and 2 sixes. He and Phil Hughes had a world record partnership of 163 runs for the 10th wicket. The crowd and players gave a standing ovation to Agar as he walked back to the pavilion after falling to a pull shot off Stuart Broad.
It was heartbreak for the youngster having come so close to a historic hundred. However, his efforts with the bat gave Australia a 65-run first innings lead. 98 is also Agar's highest first-class score, bettering 71 not out. Before this match, he had played only 10 first-class matches.
Australian Prime Minister called Agar's innings as "stunning, gutsy and agonising." He tweeted: "What a stunning, gutsy, agonising 98 from Ashton Agar in the Ashes Test."
What a stunning, gutsy, agonising 98 from Ashton Agar in the Ashes Test. Full marks to Hughes. Well done guys. KRudd— Kevin Rudd (@KRuddMP) July 11, 2013
The overall previous best by a No. 11 batsman in Tests was West Indies' Tino Best's 95 last year against England at Edgbaston, Birmingham.
Warwick Armstrong, also of Australia was the previous highest scorer at No. 11 as a debutant with 45 not out. He had scored those runs against England in Melbourne in 1902.
Agar, a specialist left-arm orthodox spinner, was handed debut by Australia on the opening day on Wednesday. He was given the Baggy Green Cap by former fast bowler Glenn McGrath.