Woodhouse capitalised on a lacklustre display from World Grand Prix champion De Decker, who becomes the second seed to fall in the tournament.
Ryan Joyce also advanced after defeating Darius Labanauskas 3-1, James Hurrell took out Jim Long 3-0 and Kevin Doets won an all-Dutch affair 3-1 against Noa-Lynn van Leuven.
Catch up on all the action from Tuesday's afternoon session at Alexandra Palace:
De Decker 1-3 Woodhouse
Woodhouse continued where he left off yesterday. Namely with good darts. He won his first leg easily and in the second leg he grabbed the break right away.
A 170 didn't go out yet, but 25 did via double eight. Woodhouse cashed in on that break by hitting double 10. Decker missed a lot of dimes and was no match for himself.
That was also the case in the second set, as De Decker only scored 80 average. He won the first leg, but then lost the set.
Woodhouse threw out 105 in the second leg and then took the break. De Decker missed three darts on double eight and Woodhouse hit double one to lead 2-1.
He then got two set darts from 60 and threw his last dart into double 10 and more than deservedly took a 2-0 lead in sets.
Decker was thus completely under pressure, but managed to start the third set well. He grabbed a very important break from 68, while Woodhouse was waiting for a double.
He opened evenly with 180 and eventually went out in 11 darts via double 16. De Decker made a statement as the third leg also went out in 11 darts to make it 3-0 for the Belgian in Woodhouse's set: 2-1 in sets.
He continued well in the fourth set as he made it 1-0 in his own leg. He again threw out double 16 and put the pressure back on Woodhouse. The Englishman made it 1-1 by throwing double four.
De Decker threw a poor third leg and gave away three chances to Woodhouse to take the break. He also took the break with double 4 and could start throwing for the match. De Decker was balancing on the brink.
Woodhouse won the match by throwing out 90 and caused a surprise. 3-1 in sets.
Joyce 3-1 Labanauskas
Joyce and Labanauskas reached a very high level in the first set, in which they both got above 100 average. Joyce opened the match with a superb 126 finish to make it 1-0.
He then grabbed the break via double 16 and cashed in that break by throwing out double 18. Thus, despite the good play of the man from Lithuania, it became quite easy 1-0 for Joyce in sets.
But as easily as Joyce won the first set, Labaunauskas won the second. He threw out double 8 in the first leg and then took a break lead by first throwing 180 and then double 10.
He took the set in via 52 and so it was 1-1 in sets. In the third set, things were evenly matched. The first three legs went with the darts and so Joyce led 2-1. He had a chance at 158 in the fourth leg, but missed double 18 for the set.
A whole handful of darts was also wasted on him, but he was allowed a third return and then threw double four to move to 2-1 in sets.
In the fourth set, Joyce immediately missed two chances to break from 25 and Labanauskas responded well. He threw out 80 and kept his own leg.
Joyce kept his leg and put full pressure on the Lithuanian. Labanauskas missed an arrow on double 16 and failed to throw out 62. Joyce hit double eight to take a 2-1 break lead and match point.
Joyce missed his first match dart from 80, but Labanauskas did not finish 100 and missed double 10. Joyce hit the double and so won 3-1 in sets to face Danny Noppert in the second round.
Doets 3-1 Van Leuven
Doets started the match strongly and was already out in 13 darts via tops. It was also in Van Leuven's leg and so that meant the break right away.
Van Leuven immediately grabbed the rebreak through a good second leg and threw out 80 via double 10. Van Leuven punched through, as 120 also went out in the third leg to take the lead: 2-1.
Van Leuven got a set dart from 72, but missed tops. Doets did the same from 80 and so three more chances came. Via tops (double 20), it became 1-0 in sets for Van Leuven.
In the first leg of the second set, Doets was again out in five innings and made it 1-0 via double 10. However, Van Leuven continued to finish very well and threw another 120 to make it 1-1.
Van Leuven threw her first 180 in the third leg and took the initiative in Doets' leg. She got three darts on the break, but Doets also missed three chances.
Van Leuven got new chances on double 8, but also failed to get it out. Doets also did not get 10 out, the tension was full on. Van Leuven missed the single one on five and Doets then did not get double one out.
Both of them failed to throw double 1 again the next turn. In the end Doets won the leg and that was necessary to stay in the set. Doets won the set by throwing out 74.
Doets started the third set by hitting 80 to take the break. He cashed in that break by hitting 51 to come close to winning the third set. Van Leuven made it 2-1 with double 10, but failed to take the break.
She missed two chances from 64 and Doets took advantage, hitting double 10 to make it 2-1 in sets. Doets held its own leg in the fourth set and failed to break with two chances.
Doets made it 2-1 by hitting 76 to move to match point. Van Leuven started leg four with two 180s, but did not throw a nine-darter. She did make it 2-2, but needed a break in the fifth leg.
Hurrell 3-0 Long
Hurrell started the match well as he threw out 120 in the first leg to make it 1-0. Hurrell threw the first maximum score in the second leg and made it 2-0 by throwing out 60, which was the break.
Long had chances for the rebreak in the third leg via tops and double 10, but missed both chances. Hurrell took the set by throwing tops in the third leg.
In the second set, Hurrell grabbed the break right away again. He hit his second maximum score and made it 1-0 with tops. He cashed in on the break by hitting tops again.
In the third set, Long also threw his first 180 and won his first leg by hitting double 1: 2-1. Hurrell took the second set by throwing his third 180 in the fourth leg and finishing on tops. 2-0 in sets for the Englishman.
Long gave the match away for good in the second leg of the third set. Hurrell won his first leg and took advantage of three misses on Long's double. He threw out double 18 to lead 2-0 in the set.
Hurrell missed seven match darts, but threw out double five with the eighth chance.
