First off this can be done in either Player or Ranked match, might as well do it in Player as that way you can invite friends in to play.
Although it's recommended to find 3 others with the game willing to boost with you it's not needed. In fact when I got this achievement I did it by simply inviting people I found online in to my game. As soon as 3 people had joined I started a game of 5 rounds, all to score 100,000 points first to win.
After I had won all 5 rounds the achievement unlocked. The process takes about a minute, the difficulty is finding friends to boost with or hoping others are online playing casually.
Edit - Doominatorx6's comment is worth reading. This is what he said "Might want to add if anyone leaves, it doesnt count. Its a big piss off when your on round 5/5 and some loser quits."