The Falcons caught their hosts cold within 90 seconds when Ollie Phillips scored a try converted by Toby Flood.
The visitors went further ahead when hooker Matt Thompson crashed over for a 12-3 half-time lead.
Gloucester rallied as Simpson-Daniel scored his first try and two missed drops from Flood left the door open.
Newcastle coach John Fletcher:
"We were shaky in the last five or 10 minutes and I wasn't too happy with some of the crucial decisions that went against us. "I had a word with the referee afterwards and I will have to look at them again.
"I'm not whingeing. We got beaten heavily last week and I thought the referee was outstanding, but today he made some poor decisions at the end that cost us.
"We're bitterly disappointed. When they score in the last minute of the game to equalise, you do feel robbed.
"Gloucester are a good side with lots of internationals, and that was probably our best performance (of the season)."
Gloucester: Balshaw; Pryce, Simpson-Daniel, Allen, Foster; Paterson, Lawson; Dickinson, Paul, Califano, Bortolami (capt), James, Strokosch, Qera, Balding.
Replacements: Titterrell, Forster, Pendlebury, Narraway, Cooper, Walker, Bailey.
Newcastle: May, Phillips, Visser, Jones, Rudd, Flood, Charlton, McDonnell (capt), Thompson, Wilson, Perry, Sorenson, Parling, Wilson, Winter.
Replacements: Long, Ward, Oakes, Williamson, Grindal, Tait, Dehaty.
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