Al Horford activated by Hawks

With the Atlanta Hawks facing what amounts to a must-win situation Sunday, Al Horford was activated by the team for Game 4 against the Boston Celtics and checked in midway through the first quarter.

Horford tore his left pectoral muscle in January and was not expected to be back for this series, but with Atlanta's season hanging in the balance, he decided to give it a go off the bench.

Horford finished with 12 points and five rebounds over 20 minutes in the Hawks' 101-79 loss Sunday.

Josh Smith, who missed Game 3 with a left knee injury, was back in the starting lineup Sunday and chipped in 15 points, 13 rebounds and five assists.

Zaza Pachulia and Jerry Stackhouse were the inactives for Atlanta.

The Hawks trail the Celtics 3-1 in the best-of-seven series.

ESPNBoston.com's Chris Forsberg contributed to this report.