In other friendlies, Paraguay played out a 2-2 draw Ivory Coast while Chile scraped past Northern Ireland 1-0. In their final warm-up game prior to the World Cup, an off-colour England needed two own goals from Japan for their 2-1 win over the Asian giants.
Centre back Gallas, who had been a doubtful starter for the World Cup because of a sore calf muscle, reassured coach Raymond Domenech by heading home a Yoann Gourcuff free kick on 63 minutes to save the ex-world and European champions from defeat. Tunisia fought bravely, opening the scoring on five minutes through forward Issam Jemaa, but France improved gradually.
As against Costa-Rica, forward Thierry Henry started on the bench, leaving his armband to left back Patrice Evra, and came on for the second half.
Meanwhile, Paraguay scored twice in the last 15 minutes as they came from behind to draw 2-2 with Ivory Coast in a friendly on Sunday and deny Sven-Goran Eriksson a winning debut as coach of the African side.
Didier Drogba gave the Elephants the lead early in the second half and former England coach Eriksson, taking charge for the first time less than two weeks before the start of the World Cup, looked set to celebrate a win when substitute Souleymane Bamba made it 2-0.
Argentine-born Lucas Barrios pulled one back with his second goal in as many appearances for the South Americans, who began with a second string line-up, and Aureliano Torres snatched a last-gasp equaliser with a deflected free kick.
Chile warmed up with a narrow 1-0 win over Northern Ireland on Sunday.
England needed two own-goals to come from behind and beat Japan 2-1 in their final World Cup warm-up on Sunday, with none of the outsiders for places in South Africa able to stake an irresistible claim.
In a low-key, disjointed match which featured another penalty miss by Frank Lampard, Fabio Capello was given little help if he was still unsure which seven players to jettison from his 30-man squad on Tuesday or even which formation to use.
The Italian had a 30-minute second-half flirtation with the impressive Wayne Rooney as a lone striker supported by Joe Cole but soon reverted to England's traditional 4-4-2. Neither approach produced a goal for a man in a red shirt as Japanese defenders Tulio Tanaka and Yuji Nakazawa both put through their own net in the second half after Tulio had given them a sixth-minute lead.
