In second place behind Majerus (Boels Dolmans) was Barbara Guarischi (Velocio SRAM) while Lucy Garner (Liv-Plantur) finished third.
"It was a good day, exactly as we planned it and it's always nice when that happens,” Majerus said.
"I was so well protected by my team-mated that I couldn't not win! We had a close look at the finish in advance and that last chicane suited me because I am pretty good at cornering.
“When I got through the corner and saw the gap I realised this might be my day so I just went for it.
"The yellow jersey was a nice bonus. I definitely wanted to try and win the stage but it was only when I was sitting at the podium waiting for the presentation that I got told I was the yellow jersey as well."
Heather Fischer (USA) and Chloe McConville (Orica-AIS) and Sharon Laws (Bigla) engineered the break of the day and crafted a three minute lead on the peloton before they were caught with just four kilometres left to race.
Majerus is now three second ahead of Jolien D'hoore (Wiggle Honda) with Lisa Brennauer (Velocio-SRAM) just one second further back in third place
Stage Four, a 103.4km run between Waltham Cross and Stevenage is likely to end in another sprint but with the overall general classification so close and bonus second up for grabs every second counts.
“The whole GC is really close. It’s all within a few seconds, so anything can happen now,” D'hoore said. “The most important day is Sunday, but we’ll try to do something tomorrow, and try to shake up the GC.”
Stage 3: 138.3km, Oundle - Kettering
1 Christine Majerus (LUX) Boels Dolmans 3hr 43min 5sec
2 Barbara Guarischi (ITA) Velocio-SRAM 0:00:02
3 Lucy Garner (GBR) Liv-Plantur
4 Hannah Barnes (GBR) Unitedhealthcare m
5 Emma Johansson (SWE) Orica-AIS
6 Lisa Brennauer (GER) Velocio-SRAM
7 Jolien D'Hoore (BEL) Wiggle Honda
8 Trixi Worrack (GER) Velocio-SRAM 0:00:05
9 Amalie Dideriksen (DEN) Boels Dolmans
10 Simona Frapporti (ITA) Ale Cipollini
1 Christine Majerus (LUX) Boels Dolmans 9hr 46min 9sec
2 Jolien D'Hoore (BEL) Wiggle Honda 0:00:03
3 Lisa Brennauer (GER) Velocio-SRAM 0:00:04
4 Emma Johansson (SWE) Orica-AIS 0:00:09
5 Barbara Guarischi (ITA) Velocio-SRAM 0:00:10
6 Lucy Garner (GBR) Liv-Plantur 0:00:12
7 Hannah Barnes (GBR) Unitedhealthcare 0:00:13
8 Simona Frapporti (ITA) Ale Cipollini 0:00:19
9 Alexis Ryan (USA) Unitedhealthcare
10 Pascale Jeuland (FRA) Poitou-Charentes.Futuroscope.89