A stoppage-time equaliser from substitute Jack Redshaw earned Morecambe a point at Oxford.
Redshaw nodded in Robbie Threlfall's corner deep into added time.
Earlier, Alfie Potter had put the home side in front on the hour mark with an angled shot that Shrimps goalkeeper Barry Roche was unable to keep out.
Potter and Morecambe's Stewart Drummond missed free headers as both sides' slim play-off hopes were dented further by an unhelpful Good Friday draw.
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Morecambe manager Jim Bentley told BBC Radio Lancashire:
"It was a great corner from Robbie Threlfall and Jack's got himself in the right position again.
"We've come away with a point that, on the balance of play, maybe wasn't deserved.
"Oxford had the better chances. They got their noses in front and you're just hoping that you get one more chance. At 1-0, you're still in the game."