Espanyol, Real Mallorca and Sevilla also booked their places in the last 16 with victories.
The rest of the second legs are to be played on Wednesday and Thursday before the start of Spain's two-week winter break.
Rafael Varane and youth-team forward Joselu scored either side of Acoran's goal for the visitors, before the busy Callejon raced away to net his third of the tie and ninth in all competitions at the end.
"I like the player and his style of play," Real coach Jose Mourinho said of the 24-year-old after his La Liga leaders wrapped up a 7-1 aggregate win.
"He has a strong personality, he knows the club and the coach at Espanyol has done a good job with him."
"We played a good game today but I need time to get back to 100 percent after seven months without playing," Sahin told reporters.
Financially-troubled Real Mallorca came back from a 1-0 first-leg deficit to win 2-0 at Sporting Gijon thanks to an own-goal by Alejandro Menendez and Emilio Nsue's second-half strike.
The La Liga side made the extra man count as Vladimir Weiss opened the scoring three minutes later and a late double from Celta's David Rodriguez was too little too late for the visitors after a goalless first leg.
Last-season's semi-finalists Sevilla were 2-1 winners at home to third-tier San Roque in the late kick-off.
