New striker Gary Twigg earned United a precious opening-day victory with an injury-time penalty at the Kassam Stadium.
Twigg, who joined Oxford in the summer from Airdrie, won the spot kick after controlling Matt Day's shot before rounding keepeer Ryan Robinson, who brought him down.
The Scotsman was under a lot of pressure, but buried the penalty into the bottom left corner.
It looked as though the U's might rue missing two good late chances.
In the 87th minute, Twigg himself, put through by Eddie Anaclet, saw a left-footed shot well saved by Robinson.
And then from Twigg's low cross from the left, Yemi Odubade blazed over.
Everyone in the stadium paid tribute to the Oxford United groundsman David Wedge, who died suddenly last weekend, with a minute's applause before kick-off.
Jim Smith selected pacy new signing Joel Ledgister, a summer capture from Ebbsfleet United, to partner Rob Duffy up front, and giant French defender Arthur Gnohere got the nod at the back ahead of Mickey Corcoran.
The best chance of the first half fell unquestionably to Rovers fullback Alex Lawless, who ghosted in unnoticed when Mark Beesley slipped a past beyond the U's defence. Lawless only had the keeper to beat from eight yards but Billy Turley spread himself quickly for a superb save.
The Yellows immediately returned to the other end and Robinson had his work cut out to deal with an angled header by Gnohere from Barry Quinn's free-kick.
Yemi Odubade replaced Ledgister for the second half which United again began well.
Eddie Hutchinson was very close to putting Oxford in front when he climbed superbly to meet Day's long free-kick with a cushioned header, only to see it just clear the bar.
Stuart Fleetwood tested Turley with a powerful angled shot, but Oxford's Matt Day went even closer to breaking the deadlock 20 minutes from the end with a rocket of a left-foot drive which smacked against the bar.
Odubade then cut in from the left to hit a smart shot, which Robinson just managed to tip over the bar.
Forest Green also rattled the crossbar, with substitute Lee Dodgson heading over Turley, but against the woodwork.
Oxford Utd: Turley, Anaclet, Day, Quinn, Gnohere, Jeannin, Hutchinson, Standing (Pettefer 66), Trainer, Ledgister (Odubade h-t), Duffy (Twigg 66). Subs not used: Tardif, Corcoran.
Forest Green: Robinson, Lawless, Jones, Preece, Tonkin, James (Afful 64), Brough, Clist, Stonehouse (Dodgson 68), Fleetwood, Beesley (Pitman 71). Subs not used: Giles, Brown.
Referee: Gary Sutton (Lincs).
Att: 5,521
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