The result was never in doubt once West Indies fell apart after choosing to bat first, with only three players reaching double figures in a paltry total of 112. Shahid Afridi (4-30) took his tournament-leading tally to 21 wickets as Pakistan's three spinners finished with 8-64 combined.
After taking two wickets, Mohammad Hafeez (61 not out) opened the batting with Kamran Akmal (47 not out) and shared a 113-run partnership to guide Pakistan to victory with almost 30 overs to spare.
"The people of Pakistan pray for us every ball," said Hafeez, adding that his bowling gameplan was simple. "Today I just tried to go straight for the line and it worked for me."
His batting also got Pakistan away to the ideal start after his slow start to the tournament.
"I was a bit unlucky in the start of the tournament, but form came back at the right time."
Pakistan will face fierce rival India or a rematch with defending champion Australia in next Wednesday's semifinal in Mohali.
The advent of the knockout rounds at the World Cup was supposed to eliminate the mismatches that affected the group stage, but that didn't prove to be the case in the first of the quarterfinals.
West Indies captain Darren Sammy had warned before the game that if his batsmen collapsed as they did against England and India in their two previous games that they would be "going home." His words proved prophetic.
Only a stubborn partnership by Shivnarine Chanderpaul and Ramnaresh Sarwan prevented a quicker demise. Chanderpaul was unbeaten on 44, but he needed 106 balls to get there.
West Indies' total was its ninth lowest in ODIs, and only just beat its lowest World Cup total of 96.
Pakistan was ruthless in its run chase, racing to 25 in the first two overs. Hafeez added an effortless 61 to his bowling figures of 2-16 off 10 overs.
The day began well enough for West Indies when Sammy won the toss and chose to bat on a slow-paced pitch. He obviously didn't account for the West Indies batsmen throwing away wickets in the manner they did.
Chris Gayle returned to the top of the order having missed the game against India but after thumping two fours, he was gone by the end of the third over, mistiming a lofted drive off Gul that went straight to Afridi at midoff.
Fellow opener Devon Smith never looked comfortable against either of Pakistan's opening bowlers Umar Gul and Hafeez. It was Hafeez who had him trapped lbw in the sixth over. Darren Bravo followed Smith back to the dressing room in the same over to another lbw decision.
At 16-3, the lowest score at Mirpur looked under threat. That was the 58 Bangladesh managed in the group stage - against West Indies. However, the experienced heads of Sarwan and Chanderpaul began an exercise in occupying the crease.
At one stage there were 19 straight dot balls and by the end of the 12th over, West Indies' runrate was 1.83. Sarwan's glance down to fine leg in the 13th over was his team's first boundary since Gayle's in the third.
Sarwan made a tortuous 24 off 68 balls but the hard work went to waste when he played a loose drive straight to Umar Akmal at point to give Afridi his 18th wicket of the tournament - and more quickly followed.
Kieron Pollard and Devon Thomas fell in the space of two Afridi balls in the 27th over, and West Indies proved no more adept in dealing with the offspin of Saeed Ajmal, who accounted for Sammy and Davendra Bishoo in the next over.
That made it four wickets in nine balls and left West Indies on 71-8.
Chanderpaul, who was back in the team after being left out of the last two games, and Roach took West Indies past the 93 it managed against Kenya at the 1996 World Cup, but there was little else to celebrate.
The outstanding Afridi finished off the innings in the 44th over by bowling Ravi Rampaul for 0.
Hafeez, opening the batting as well as the bowling, stroked two fours in the first over of Pakistan's innings to set the tone for an embarrassingly easy chase.
