The northern summer signing from Manchester City steered home a 31st-minute free-kick that secured all three points for last season's runners-up.
Atalanta made an unexpected run to fourth place - and UEFA Europa League football - last term but the Bergamo outfit could not avoid defeat as substitute Josip Ilicic failed to salvage a point when he slammed the ball against a post with three minutes remaining.
Francesco Totti, who retired at the end of the 2016-2017 campaign after 24 years as a Roma player, watched from the stands in his new role as a director.
