San Jose continued to dominate the remainder of the first half, with Zusi, Dominic Dwyer and Zizzo all going close.
The second half followed a similar pattern, as Opara saw his shot from close range saved by San Jose goalkeeper Busch.
The home side eventually went ahead in the 57th minute from the penalty spot.
Steven Lenhart committed a handball offence, and Dwyer made no mistake from 12 yards.
Dwyer had a good chance midway through the second half from a narrow angle, but failed to keep his final effort on target.
San Jose rallied in the final 20 minutes to pick up a point at Sporting Park, with Chris Wondolowski going close, but they failed to rattle their hosts.