Philadelphia vs. Boston and L.A., 1980 Eastern Conference finals and NBA Finals
The NBA was basically a three-team league in 1979-80: The Celtics, Lakers and Sixers won 61, 60 and 59 games respectively, but no other team cleared 50. L.A. and Boston won with offense, finishing first and second respectively in offensive efficiency thanks to Magic and Bird, but the Sixers were the opposite -- a defensive juggernaut that ranked first on that end of the floor.
In the playoffs, the Sixers came away with a split. In the conference finals, Philly's D prevailed, absolutely suffocating the top-seeded Celtics. Boston was held nearly 20 points below its season average in the series, even failing once to clear the century mark in an era when reaching 100 points per game was routine.
But they didn't do as well in the Finals against L.A. The Lakers got their numbers, Magic went off in the clinching Game 6, and L.A. had its first of five titles for the decade.