Horford struck for 22 points and hauled down 11 rebounds to pace Atlanta, which broke a close game open with a big fourth quarter.
Smith accounted for 21 points, seven boards and five assists as the Hawks continued their recovery from a stretch that saw them lose six times over a seven-game span.
The Nets, meanwhile, fell for just the second time in six outings despite 18 points from former Hawk Joe Johnson.
Exploding whale video goes viral on Internet
Sign language interpreter at Mandela service called out as fake on Twitter