Povetkin, 32, became the second active Russian fighter to hold a world heavyweight title along with compatriot Dmitry Pirog following his defeat of Uzbekistan's Chagaev over 12 rounds.
Chagaev was under severe pressure from the first round, often succumbing to Povetkin's left-handed uppercuts as the Russian's speed and agility gave him the advantage.
However, the defending champion fought back admirably in the sixth round, and gave Povetkin plenty to think about with several testing left-handers.
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Povetkin kept his edge and regained control of the match in the final few rounds, and Chagaev's late volley of blows in the final round was not enough to avoid defeat.
The judges awarded the fight to Povetkin with two scores of 117-113 and another of 116 112, taking the Russian's professional record to 22 wins, no losses and 15 knockouts.
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