Pakistan won the toss and selected to bowl initial and solely Lendl Simmons offered any real resistance because the hosts were dismissed for 220 from their fifty overs.
In reply, Shehzad created his 102 from solely 148 balls because the tourists reached 223 for 3 within the forty eighth over.
Pakistan currently lead the five-match one-day series 2-0.
West Indies never extremely recovered from a disappointing begin, and though opener Simmons (51) offered some resistance they lost wickets at regular intervals with Mohammad Hafeez, Wahab Riaz, Saeed Ajmal and Shahid Afridi all taking 2 wickets every.
Shehzad then struck his second one-day international century as Pakistan continued where they left off within the initial game in St Lucia where they won by eight wickets.
The 19-year-old shared 3 successive half-century partnerships with Mohammad Hafeez (32), Asad Shafiq (23) and Misbah-ul-Haq (43 not out) that place Pakistan firmly not off course for victory.
He glanced a delivery within the forty fourth over from Dwayne Bravo to deep fine leg for one to succeed in his milestone from 143 balls, before turning into the second wicket for Devendra Bishoo.
Umar Akmal carried the guests over the edge with twelve balls remaining when he lofted a delivery from Dwayne Bravo to long-off for the ultimate boundary of the match.
Pakistan have currently won their last seven ODIs against West Indies, a sequence unfold over the last four years.
The third one-day international takes place in Barbados on Thursday.