Bicester paid the price for a lacklustre first half performance when they went down 36-24 at home to Thatcham for just their second league defeat since November.
The incisive visitors ran in four first half tries before a fifth try shortly after the break gave them what looked an unassailable 29-5 lead, but Bicester fought back brilliantly to touch down three tries and earn a well-deserved bonus-point, although their fightback came too late to prevent defeat.
Eight minutes from kick-off, Thatcham went ahead after Bicester conceded three successive penalties on the left, which led to Tom Bestwick plunging across from a driven line-out.
The visitors quickly added a second try when a combination of slick handling and weak Bicester tackling resulted in Louis Kanaar-Brown racing over and with fly-half Joe Leadley converting both tries, Thatcham held an early 14-0 lead.
Bicester rallied and put their first points on the board when lock Matt Dye was sent crashing over in the corner, but Tom Miles missed the conversion and within 10 minutes Thatcham took advantage of more poor Bicester defending with Leadley powering 20 metres down the right for a third try.
The visitors remained on the front foot and they increased their lead to 19 points at half-time after Bicester lost their own scrum and Thatcham scrum-half Luke Evans dotted down.
After the restart, Thatcham quickly increased their advantage to 24 points when a penalty was fired into touch and from the resulting line-out, James Thorogood was driven across.
Bicester looked down and out at this point, trailing 29-5, but they kick-started a terrific fightback when a Thatcham scrum was heeled against the head and strong running from Andrew Cook led to a scrum, from which the hosts were awarded a penalty try.
Miles converted and moments later flanker Dan Spencer went on a quick burst down the left side before the ball was transferred across the field to where Miles sent lock Ryan Gallacher hurtling across in the corner.
Bicester now trailed by 12 points but just as it seemed they were building some momentum, the visitors were awarded a penalty try of their own with Leadley’s conversion all but sealing victory.
The home side had the final say, however, as Spencer broke sharply from a scrum on the right and after good play by Jim Farrow, Miles and centre Francois Wiese, Walsh touched down for a bonus-point try, with Miles brilliantly adding the extras.
Bicester continued in the driving seat for the remaining 15 minutes but were unable to breach the Thatcham defence as the visitors ran out winners after an entertaining contest.
Bicester, who have dropped a place to seventh in the Southern Counties North, host Drifters this weekend.
Elsewhere, Bicester IIs drew 17-17 with Reading IIIs, while the IIIs were beaten 38-13 by Buckingham IIIs.