League Two leaders Oxford smashed a trio of first-half goals to claim a 3-0 Kassam Stadium win that left Morecombe reeling.
James Constable grabbed his 101st goal for the club on 16 minutes, bundling the ball in off his knee after Barry Roche parried Michael Raynes' header.
Sean Rigg made it two nine minutes later with a far-post finish after Ryan Williams had beaten Morecambe's offside trap and then sprinted down the right.
And on-loan Fulham winger Williams further increased Oxford's lead in the 31st minute with a classy chip over keeper Roche after Asa Hall's defence-splitting pass.
Chris Wilder's men were totally dominant before the break and Hall also headed against the bar at a corner.
Morecambe made a better fist of it in the second half as Jack Sampson saw a low 18-yard drive come back off the post, while Marcus Marshall and Andrew Wright forced Ryan Clarke into saves.
Despite Oxford's flying start to the season - mainly down to their red-hot away form - this was only a second win in their last 10 games at home.