The Nigerian got the curtain raiser in the MCH Arena with a brilliant individual effort in the 19th minute but was cancelled two minutes later by Marvin Pourie, as both teams settled for a tie in half-time.
Eight minutes into the second half, Jonas Borring sealed maximum points for the Wolves with the match winning goal as Randers continue their unpleasant run of two losses and a draw in three games.
Onuachu will be aiming to surpass his tally of 18 goals in 36 league games in the last campaign as Midtjylland sit in the fourth place with six points from three games in Superliga log.
Compatriot Rilwan Hassan was later introduced for Simon Kroon in the 62nd minute as Onuachu paved way for Jakob Poulsen in the 76th minute.
Jess Thorup’s men welcome Arka Gdynia for the second leg of their UEFA Europa League qualifiers before visiting FC Helsingør for their next league game on August 6.