Trying to build on their road win over the Eagles, the Titans went home for a Week 12 fight with the New York Giants.  In the first quarter, Tennessee trailed early as QB Eli Manning completed a 3-yard TD pass to WR Plaxico Burress for the only score of the period.  In the second quarter, Giants RB Brandon Jacobs got a 10-yard and 4-yard TD run to give the Giants a seemingly comfy 21-0 halftime.  After a scoreless third quarter, the Titans' improbable comeback began in the fourth quarter with 10 minutes remaining.  QB Vince Young completed a TD pass to TE Bo Scaife.  Afterwards, Young would follow it up with a 1-yard TD run.  The key play of the game came on a 4th and 10 from Tennessee's 24-yard line, when Giants DE Mathias Kiwanuka actually had Young in his grasp, but he let go because he was afraid that he would get a Roughing the Passer penalty.  It allowed Young to dash away for the first down.  Four plays later, he would complete a 14-yard TD pass to WR Brandon Jones.  Afterwards, after Manning got intercepted by CB Pacman Jones (who intercepted Manning earlier in the game), it would lead to the game-winning field goal, as kicker Rob Bironas nailed it from 49 yards out.  With the win, the Titans improved to 4-7.. In which quarter did the key play of the game occur?