Even though the Mavericks got swept, they took fought OKC tip to buzzer in three of those games with a team that's not half of what the Spurs are. The Spurs have ZERO weaknesses, are the most versatile team in basketball, the deepest team in basketball, and have the best coach of all time coaching out of his mind right now. OKC are a bunch of young and very talented players whose skill-sets overlap that make a lot of mistakes, still.
Maybe OKC beat San Antonio, but there is PLENTY of evidence to suggest that the Spurs will take those kids to school. The Spurs are on a mission this year.