Ryan Christie had given the home side an early lead only for substitute El Alagui to notch his third league goal of the season four minutes after entering the field of play as a substitute.
Christie had the game’s opening effort early on and fired high and wide but the midfielder did not have to wait long to notch the second senior goal of his career.
Watkins careered down the right flank in the seventh minute and crossed for the 19-year-old to head home into the bottom-left corner past the outstretched arms of Radoslaw Cierzniak.
Dundee United upped their tempo in an effort to get back on level terms with Nadir Ciftci and Ryan Dow both forcing saves from Dean Brill
Gary Mackay-Steven, who was substituted at half-time due to injury, went close for United just before the end of half but his effort went wide of Brill’s left-hand post.
United came straight out of the traps after the break with Ryan Gauld narrowly missing to the left directly from a free-kick after Paul Paton was brought down unfairly.
Brian Graham mustered the first shot on target in the second half for United but Brill comfortably saved the 26-year-old’s effort from distance.
Ciftci and Graham both had further chances for the away side but were unable to find the target.
El Alagui replaced Gauld in the 67th minute and four minutes later the Frenchman forced an equaliser. Sean Dillon slipped the ball to the 19-year-old inside the area and he emphatically fired home past Brill.
Buoyed by the equaliser United created opportunities for Ciftci, Graham and El Alagui, all of whom were unable to trouble Brill.
Christie and Aaron Doran both had chances for the home side towards the end, but were unable to take advantage as the game ended in stalemate.