The Robins surrendered a half-time lead on Saturday for their first league defeat since September.
Bideford suffered their first league defeat since September at North Leigh on Saturday.
The Robins were beaten 4-3 in Oxfordshire in the Evo-Stik League South West fixture after giving up three goals in the space of eight minutes in the second half.
A Craig Duff double took the visitors into the break with a 2-1 lead. The striker scored after 16 minutes; and after North Leigh equalised through George Seacole seven minutes before the break, Duff headed the Robins back in front a minute later.
It all went wrong nine minutes into the second half. First Matt Grabe got North Leigh and equaliser with a left-footed strike, and four minutes later, Dejon Noel-Williams rounded Steve Oliver to give them the lead.
Seacole added his second and the hosts’ fourth on 62 minutes.
James Mayne pulled one back for Bideford in the 90th minute, but it was too late for the Robins to go on and salvage a point.
Bideford manager Sean Joyce said: “We should have come in at half time five or six up.
“We created chances and missed some good chances – it was too easy.
“We went out in the second half and expected it to be easy again.
“At half time we said go and get 10-15 minutes under our belts and we’ll see the game through and they came out and had a go at us. The damage was done in that eight-minute spell.
“We made mistakes and got punished by them, but it should have been out of site at half time really.”
The Robins went into the game without new signing Liam Gregory, and they will be without him for some time after the full-back suffered a broken leg in their 1-1 draw at Mangotsfield United last week.
The Robins were due to play Stoke Gabriel in the Devon St Luke’s Challenge Cup tonight (Tuesday) but were rained off.
On Saturday, Joyce’s side welcome Cinderford Town to the Sports Ground and the manager is keen to get his side back on another winning run and consolidate their playoff spot.
“Maybe we are ahead of where I want to be,” he said.
“When you look at the transition we have had, with a lot of players coming over from Barnstaple and a few from lower leagues, to say we are fifth in the league, I think the lads have done a tremendous job.”