Substitute Ashley Nadesan saw red early on in a feisty second-half but ten-men Crawley stood firm for a valuable point.
The forward had replaced defender and goalscorer Joel Lynch, who was forced off with an injury at half-time.
Right-back George Francomb also came off injured in a dramatic first-half, which saw the Reds come from a goal down to lead at half-time.
Following the two injuries, and red card, a number of players played in makeshift positions and put in extra defensive work to grind out a draw.
Here’s how we rated John Yems’ men.
1. Glenn Morris - 7
Routed to the spot and helpless to stop early opener. Diving save to prevent a looping, deflected effort. Couldn't have done anything about the second goal either. Great save late on.
Photo: Steve Robards
2. George Francomb - 6
The August player of the month looked his assured self at right-back before he was forced off with an injury.
3. Joel Lynch - 8
A superb double block kept Crawley in the game before he brought the Reds level with his first goal for the club after a corner. Earned applause from the home support after putting in a strong challenge up the other end. He is quickly becoming a fan favourite. Appeared to be struggling with an injury late in the first-half and he didn't return after the break.
4. Tom Dallison - 8
Assured and composed in his favoured centre-back positon. Extra pressure was put on his shoulders after Lynch was forced off injured but he handled it brilliantly. Recovered well after the tame early goal, with Armstrong left unmarked from a corner.