He and Waite continued to look in total control, literally bringing Somerset to their knees at times as the close fielders desperately hoped for an edge off the spinners.
Waite moved to a patient fifty before D’Oliveira’s intense feat of concentration spanning five hours and 40 minutes came to an unfortunate end.
Thrusting his front pad well outside off stump to a wide delivery from Vaughan and playing no shot, he was given out lbw when the ball turned sharply and appeared to strike his back leg.
With a third new ball due in seven overs, Somerset sensed it was a pivotal wicket and celebrated as though the game was wony, wth Worcestershire 415-7 at tea, still 101 behind.
Having employed mainly spin, including that of triple centurion Tom Banton, Somerset got through their overs quickly enough to take the new ball immediately after the interval.
Skipper Lewis Gregory shared it with Craig Overton, who struck the next blow in the fifth over after the break when Allison, on 22, fended a short ball straight to Tom Lammonby at short mid-wicket.
Still Worcestershire resisted, the obdurate Waite having been joined by Taylor and the final hour began with Somerset having a minimum of 16 overs to claim the last two wickets, while Vaughan and Leach operated with fielders clustered around the bat.
Leach ended Taylor’s stubborn effort of 12 off 68 balls when he edged to second slip with 8.3 overs remaining to give the England spinner his milestone 500th victim. But 22-year-old left-hander Hinley showed a maturity beyond his years to see out 44 balls, while Waite defied everything that Somerset could throw at him.
