ATLANTA — Al Horford snatched away an offensive rebound and dropped in the winning basket with 1.9 seconds left after Dennis Schroder’s drive to the basket was blocked by John Wall, giving the top-seeded Atlanta Hawks an 82-81 victory over the Washington Wizards on Wednesday night and a 3-2 lead in the Eastern Conference semifinals. Paul Pierce, who made a buzzer-beating winner in Game 3, appeared to have doomed the Hawks again when his 3-pointer from the corner gave the Wizards an 81-80 lead with 8.3 seconds left. Pierce taunted the Hawks bench and home crowd on his way back down the court before bowling over Wall, who was playing for the first time since Game 1 after fracturing several bones in his left hand.