Goals in each half from Adel Taarabt and Adil Rami earned Milan their fourth win in six matches under Seedorf, with Sampdoria seeing Maxi Lopez dismissed in the final 20 minutes for picking up two cautions for dissent in quick succession.
It was one of Milan's best performances of the season and, with Inter drawing 1-1 with Cagliari, leaves them five points behind their rivals in the race for UEFA Europa League qualification.
The Dutchman, who played and scored the last time Milan won in Serie A at Samp back in 2007, was pleased with his side's all-round performance.
"It was a good day for Milan in all aspects, in defence and attack," the Milan coach told Sky Sport Italia.
"The most important thing is that the squad grows, then the results will help us a lot.
"These three points will give us mental strength to take forward.
"We were good and compact and I must also congratulate (Sampdoria coach) Sinisa (Mihajlovic) for how he gets his players to play.
"Our improvement is just a matter of time. We managed to get continuity in our play out on the pitch.
"We now need to take it game by game and then we'll see where we are at the end of the season."
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