There was little to choose between the sides in the first 15 minutes apart from an electric break from Mathew Tait which ended when the England cap slipped just inside the Gloucester 22.
James Simpson-Daniel and Peter Richards looked dangerous for Gloucester, but it was Newcastle who had the first points on the board when Matt Burke kicked a 55-metre penalty shortly after missing one from 40m.
Mercier missed a chance to level from wide out but made amends when he cut through the midfield and threw out a long pass for Terry Fanolua to scramble over in the corner.
Referee Tony Spreadbury ruled the ball was correctly grounded, and Mercier converted from wide out.
Burke missed a 45m kick at goal, and Tait soon went close. The full-back chipped ahead; Jon Goodridge knocked on; then Tait hacked on and just failed to get there as the ball rolled agonisingly into touch in goal.
Following a Burke penalty at the end of the first half, Mercier missed a similar opportunity at the start of the second – and Newcastle then did well to defend a Gloucester line-out catch and drive five metres out.
The Falcons pack looked much more solid with the introduction of Davis Wilson and Andy Long in the front row.
For the first time, the Gloucester scrum looked under pressure. That led to a penalty on halfway. But Burke was just short with the kick at goal into the wind and then just left with another from halfway soon afterwards.
Newcastle were asking all the questions – and Colin Charvis, Tait and Anthony Elliott all went close before Burke’s third penalty gave the hosts a 9-7 lead.
Immediately, though, Newcastle came in from the side – and Mercier made it 10-9.
Straight from the restart Gloucester were offside, but Burke pulled the kick at goal wide with 10 minutes left.
Simon Amor caught James Grindal at the base of the scrum. The number nine was penalised, and Mercier kicked a crucial penalty.
There was almost a sensational end to the game, Jamie Noon cutting through 20m out with seconds left on the clock – and it seemed the Falcons must score. But Ben Woods could not hold on to the England centre’s pass on the line – and Gloucester survived.