Shamir Goodwin gave the visitors the lead but Eoin Doyle quickly equalised and O'Shea clinched victory with goals in the closing minutes to leave Torquay still without a league win at Chesterfield.
Northampton remain rooted to the bottom of the Football League after promotion-chasing Fleetwood ran out 2-0 winners at Highbury.
The visitors looked likely to grab an equaliser but Fleetwood finally found another gear with 11 minutes remaining.
Parkin was sent clear down the right and the striker chose o chip the ball in to the back post rather than shoot and Evans was the grateful recipient for his second of the afternoon to seal victory.
Oxford equalled their biggest home win of the season with a 3-0 victory over Mansfield to boost caretaker manager Mickey Lewis's prospects of getting the job on a permanent basis.
The U's are now unbeaten in five games under Lewis, and they simply had too much firepower for the Stags as they consolidated their place in League Two's top three.
Rochdale's pursuit of an automatic promotion place continued apace with a 2-1 win over Morecambe at Spotland.
Goals from Scott Hogan and Ian Henderson proved enough to see off the visitors, who briefly led through Jack Redshaw.
In-form Hartlepool made it three wins from five games as they brushed aside Newport in a comfortable 3-0 win.
Pools moved to the edge of the play-off zone and leapfrogging the Exiles, now winless in six, with an energetic display.
John McCombe bagged a brace as 10-man Plymouth were hammered 4-0 by York.
Dagenham battled to a 1-1 draw at high-flying Burton despite being down to 10 men for most of the second half.
Billy Kee came off the bench after the dismissal of Jack Connors to cancel out a superb Lawson D'Ath strike for the visitors.
Ryan Taylor headed struggling Portsmouth to their first home win since Boxing Day as they ground out a 1-0 win over AFC Wimbledon.
Exeter scored twice in the final eight minutes to secure their first victory of 2014 as they fought back to win 3-2 at Southend.