Steve Tikolo won the toss and having noted Ireland's brittle batting during its recent match against Namibia in Windhoek, he decided to let the visitors have first use of the track. And with Ireland captain William Porterfield back in the pavilion having scored just a single and the score 19-1, that decision initially looked justified.
But then O'Brien and Alex Cusack made the Kenyans suffer in the field, putting on an impressive 146-run partnership for the second wicket. Although he has spent most of his Ireland career to date batting at four, O'Brien has been opening the batting well for Northamptonshire in the English County Championship and has now managed to transfer that success to the international stage.
The 26-year-old Dubliner was very much the dominant partner with Cusack contributing 42 (from 178 balls). After his long vigil Cusack was eventually dismissed, caught at the wicket by Morris Ouma off the off-spin of Hiren Varaiya.
But that just brought Andre Botha to the middle and the pair proceeded to add another 70 runs. O'Brien ended up with 135 before being caught at mid-off by Lameck Onyango off the bowling of Peter Ongondo. It was O'Brien's fifth century in the ICC Intercontinental Cup and his seventh first-class ton in total. Altogether he faced 235 balls and hit 17 fours in the innings.
If Tikolo and his team-mates thought things were going to get any easier with O'Brien gone, they were sorely mistaken. Botha was in fine form, stroking a 62-ball half-century and ending the day unbeaten on 65 (11 fours). He shared an unbroken 47-run partnership with Niall O'Brien's younger brother Kevin (23 not out).
On the bowling front, only three wickets fell in the day but Kenya did a good job containing Ireland's scoring. Onyango was probably the pick of the bowlers taking 1-49 off 19 overs, including the wicket of Niall O'Brien.
This is a must-win game for defending champion Ireland if it is to make it through to its third ICC Intercontinental Cup final in succession. If Kenya takes the points for securing a first-innings lead or just thwarts Ireland's attempts to win the match outright, Tikolo will the one leading his men into the final against Namibia next month.
But this has been a solid start for Ireland and with a long batting line-up it is now in a good position to press home the advantage and amass a big first-innings total. Play resumes on Sunday morning at 1000.
Note: the venue and exact date of the final will depend on the result of the Kenya v Ireland match.
The ICC Intercontinental Cup has quickly grown in stature and profile since its inception four years ago and now the ICC's premier first-class tournament is an integral part of the Associate Members' cricket schedule.
Having previously been designed around a two-group, three-day format, the event has evolved into an eight-team, round-robin and truly global tournament featuring four-day cricket which gives those teams who do not play Test cricket the chance to experience the longer form of the game.
Scotland won the first ICC Intercontinental Cup in 2004, beating Canada in the final, while Ireland has been victorious in both events since then, beating Kenya in the 2005 decider and Canada in the 2006-07 event.
For more information go to: www.icc-cricket.com