The substitute netted from close range after Nigel Pearson's men had failed to clear Ian Harte's free-kick.
It was just reward for the Royals, who had seen a Shane Long penalty saved by Vito Mannone after Paul McShane had cynically brought down the striker.
However, Hull will feel they should have claimed victory after hitting the woodwork twice through Robert Koren and Cameron Stewart.
James Harper, who spent nine years at the Madjeski Stadium, had put the Tigers in front in the first half when he drilled a long-range effort past the helpless Adam Federici.
That looked to be enough to seal the win, but Church ensured the spoils were shared as both sides extended their unbeaten streak to eight matches.
Source: PA
Source: PA