Dhawan made his first-class debut for Delhi against Andhra in November 2004, in the 2004–05 season of the Ranji Trophy scoring 49 on his debut innings. He finished as Delhi's leading run-getter that Ranji season with a total of 461 runs from 6 matches and a high score of 130, scoring more runs than experienced players in the team like Ajay Jadeja and Aakash Chopra. In the Ranji One-day Trophy that followed, Dhawan made his List A debut against Jammu & Kashmir in January 2005. He then scored back-to-back unbeaten hundreds against Himachal Pradesh and Haryana. He was picked in the India Seniors squad for the Challenger Trophy in February, in which he opened the innings against India B with future India teammate MS Dhoni. In the second match, he scored a 124-ball 126, sharing a 246-run first-wicket partnership with Dhoni who also struck a century, helping India Seniors chase down 276 for the loss of two wickets. He was selected in the India A team to play in the one-off 50-over match against the touring Pakistani team in March that year. He scored 8 before being bowled by Naved-ul-Hasan.