After marking the 34th anniversary of the Hillsborough disaster before kick-off, Liverpool took the momentum ahead of their questionable opener in the 35th minute.
Alexander-Arnold blocked Junior Firpo’s pass with his elbow before Salah could clear it out.
When Salah dropped back to Alexander-Arnold, the right-back prepared Gakpo to head home from close range.
Leeds were angered, only to go up against an investigation into the incident despite VAR protests.
It was Gakpo’s fifth goal since signing from PSV Eindhoven in January after Salah troubled Leeds.
Salah’s eighth goal in six appearances against Leeds came in brutal fashion.
Jota was allowed to move forward uncontrollably before slipping a pass to Salah, who finished with perfect accuracy.