Inter Milan have lost ground on Serie A leaders Juventus as they suffered a surprise 3-2 defeat at Atalanta.
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The loss has brought an end to the Nerazzuri's run of 11 straight wins in all competitions.
The hosts landed the first blow with nine minutes on the clock as Giacomo Bonaventura headed in Federico Peluso's cross.
Inter drew themselves level 10 minutes into the second half when Fredy Guarin powered home a free kick, but they went behind again minutes later thanks to Denis's simple finish.
Denis then extended his side's advantage from the penalty spot midway through the second half following Matias Silvestre's foul on Maximiliano Moralez.
The visitors pulled one back in the 84th minute through Rodrigo Palacio's clinical strike, but they were unable to grab an equaliser.
