Reus, however, struck five minutes after the restart with Jadon Sancho cutting back into the box and Alcacer faking a shot but letting the ball through his legs for the Dortmund captain to fire in.
In a similar move Hradecky managed to palm a Sancho cross away but it fell into the path of Portuguese Raphael Guerreiro who had no trouble tapping in the third goal after 83 minutes. Reus completed the win in the 90th with his third goal in four games.
Alassane Plea’s 14th minute goal was enough to give Borussia Moenchengladbach a 1-0 win at Cologne and lift them to seven points.
Werder Bremen beat Union Berlin 2-1 away in a lively encounter that had three penalties, two sending offs — one for each team — and four video reviews.
Leipzig, who are also on nine points, host champions Bayern Munich, who have seven, later on Saturday.