Air carrier Captain reported a near collision occurred during taxi at SAN when he spotted a corporate jet at the last moment.

Narrative

I was taxiing around 8 knots due to a flow time. About 90 feet from the intersection of B5 my First Officer (F/O) said 'there is an aircraft' and pointed to the left. I looked left but did not see the small [corporate jet] holding short of Runway 27 at B5. The F/O then pointed again and I picked up the small corporate aircraft and braked about 40 feet prior to the [corporate jet]. We had not been given instructions from ATC to hold short of B5. If my F/O had not spotted the [aircraft] and I had continued taxiing my left wingtip would have impacted the [other aircraft's] tail because it was around 20 feet short of the hold line. We waited for the [corporate jet] to cross Runway 27 and then continued our taxi. The F/O and I were both surprised at how difficult the [corporate jet] was to see even at close range. We should have been given a clearance to hold short of B5 or the [corporate jet] should have been instructed to pull up to the hold line. Although; I'm not sure we would have had clearance even if the [corporate jet] was on the hold line