In the opening match of the 2018-2019 Championship campaign Derby put in a poor first-half showing before Reading went ahead soon after the break when Jon Dadi Bodvarsson nodded powerfully home.
Derby drew level on the hour - with their first shot on target - when debutant Mason Mount drilled in from long distance.
And Tom Lawrence nodded in the winner deep into stoppage-time, just as the game looked to be petering out to a draw, sparking wild celebrations in the away dug-out.
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Former Chelsea and England midfielder Lampard, 40, arrived at Pride Park at the end of May, succeeding Gary Rowett, and took over a side that had lost in the play-off semi-finals to Fulham.
Derby's pre-season had gone well, with four wins in five matches, and Lampard gave competitive debuts to two of his five northern summer signings - midfielder Mount and winger Harry Wilson, the loanees from Chelsea and Liverpool respectively.
Reading finished in 20th place in the Championship in the 2017-18 campaign, avoiding relegation by just three points and had a poor pre-season, failing to win six games.
