* Q3 core profit 227 mln euros, vs 222 mln forecast
* All-in-1 subscriber growth 12.1 pct, vs 16.1 pct in Q2
* Happy with 878 million euros 2012 EBITDA consensus
* Increase in "All-in-1" customers slowed in Q3
* Shares up 0.6 percent (Adds CEO, analyst comment, shares)
BRUSSELS, Oct 18 Dutch cable operator Ziggo said the pace of customer growth slowed in the third quarter because it had cut back on promotional activity while rivals stepped up their game.
"The competition we are seeing is mainly the incumbent, KPN , it is Tele2 and, in a limited way, the mobile operators," chief executive Bernard Dijkhuizen told a conference call on Friday.
Ziggo said the number of clients subscribing to "All-in-1" bundles combining TV, broadband and telephony rose 12.1 percent year-on-year in its third quarter, a slowdown from 16.1 percent in the second quarter.
Dijkhuizen said Ziggo had about 26.5 percent of the Dutch market share in broadband and 35.9 percent in digital TV at the end of the second quarter.
Third-quarter core profit rose 8.1 percent to 227 million euros ($297 million), compared with a forecast for 222 million from StarMine SmartEstimate, which gives extra weight to top-performing analysts.
"The investment case remains strong simply because they have the better product but these results point out that marketing is key," Kepler analyst Matthijs Van Leijenhorst said in a note.
Ziggo shares, priced at 18.50 euros when it listed in March, were up 0.3 percent at 26.99 euros at 0755 GMT.
Ziggo reiterated that it expected to increase market share and revenue in 2012, and was confident of meeting market expectations for 2012 core profit of 878 million euros, up 5.2 percent increase.
Capital expenditure this year would be 270-280 million euros, having previously targeted 280 million, it said. ($1 = 0.7638 euro) (Reporting by Robert-Jan Bartunek; Editing by Dan Lalor) (firstname.lastname@example.org; +32 2 2876850)