The Shubham Ralhan-led Waka were dismissed for 140 in 41.1 of a possible 50 overs.
Second-drop James Birrell was their top scorer with 44 and opener Gautam Sareen made a watchful 27 off 60 balls.
Three HSOB bowlers took two wickets apiece - spearhead Steve Lamb 2-34 off 11 overs, tall leg-spinner Rhys Grogan 2-36 off 11 and medium-pacer Alex Shanks 2-11 off 2.1.
Shanks had started the game on a hat-trick after taking two wickets with consecutive balls to end OBR’s innings a fortnight ago.
François Louw, bowled first ball on debut for HSOB the week before, made 26 off 84 balls from No.6 in a vital 122 run-stand for the fifth wicket with Kumar.
Shaw acknowledged the quality of Kumar and Louw’s match-winning partnership.
“That 100 by Ajay (Kumar) - his third for HSOB - was well-controlled, the best I’ve seen, and François played with grit and concentration.”
Horouta spearhead Jagroop Singh, as usual, attacked the stumps to great effect in taking 2-37 from 12.2 overs with his medium pace.
He went through No 3 Lamb for a golden duck and Shanks for one.
Ralhan (1-26 off 9 overs), like Singh and Lamb and Shanks earlier, demonstrated that full, accurate bowling is essential on the HBR pitches.
In the other DJ Barry Cup clash, Gisborne Boys' High School First XI claimed four points - their first of the DJ Barry Cup - in their loss on first innings to OBR on HBR 2.
OBR skipper Matt Cook won the toss, chose to take first knock and his batsmen responded.
Left-hander Martin Worndl made 81 and fellow opener Bekko Page a quickfire 30 in an opening stand of 56.
First-drop Jonah Reynolds fell for four, but younger brother Harvey Reynolds, the most improved player in the Premier Grade to this point in the season, made 46 before going leg before wicket to Marcus Gray (2-56 off 11).
In-form allrounder Nathaniel Fearnley snared 3-49 off 11 and hit six boundaries in a 19 ball-dig of 37 at No.7.
Worndl and company saw OBR through to 235-6 in the 50 overs allowable but in response, Boys' High showed some fight, and were 141-7 at 6.30pm after 39 of a possible 40 overs.
Despite the craft and quality of veteran left-arm swing bowler George Reynolds (3-25 off 10), the younger team showed hitherto unseen stickability.
Opening batsman Charlie Whitfield, with 35 in a 99-ball vigil, showed pluck as he set aside shorter-form flair and batted time instead.
It took sturdy concentration to hold Reynolds and senior and new ball specialist Jimmy Holden (1-19 off 8) at bay.
Like Harvey Reynolds, Whitfield is a member of the Poverty Bay Under-16 team which contains a raft of capable batsmen who have begun their rise through the ranks.
They have a long way to go, but runs are often in short supply and - as Kumar and Worndl proved - the more time a player spends in the middle, the more productive they end up being on pitches with enough in them for everyone.
HSOB and Horouta head the DJ Barry Cup standings on 20 points apiece (HSOB have a superior net run-rate), OBR are on 18 and GBHS 4.
In Saturday’s round 4 games, HSOB face GBHS while OBR take on Horouta.
