But the Netherlands, resuming on 140 for five and needing a sustained batting performance in order to avoid the follow-on, produced exactly that, largely thanks to a record-breaking seventh-wicket stand of 160 between Max O’Dowd and Logan van Beek.
The day started well for Ireland, with Ben Cooper adding just a single to his overnight score. He was dropped by Andrew Balbirnie at second slip off Tim Murtagh, but the double-centurion made amends in Murtagh’s next over by accepting a more difficult chance in the same position.
That brought Van Beek in to join O’Dowd with 179 still needed to make Ireland bat again, but the home side would have no further success for 43 overs as the Dutch pair gave a demonstration of disciplined, positive batting in adverse circumstances.
They also exposed the limitations of an Irish attack in which only Boyd Rankin was consistently menacing. Leg-spinner Jacob Mulder came in for some particularly harsh treatment as O’Dowd went on to complete a maiden international century and Van Beek also posted his highest score for the Netherlands, making 76.
O’Dowd was the first to go, as Rankin returned with the new ball and induced a snick to Balbirnie, again at second slip. He had made 105 from 151 deliveries, with 16 fours and one six.
In his next over the tall Irish paceman struck again, this time removing Van Beek, who edged to Ed Joyce at third slip.
But by this time only 14 were needed to avoid a follow-on which was now wholly theoretical: it was hard to imagine Porterfield enforcing it after the work his bowlers had had to do.
In fact Tobias Visée and Shane Snater continued the Dutch fightback, adding another 38 for the ninth wicket, and with Visée making a valuable 30 and sharing a last-wicket stand of 23 with Quirijn Gunning, the deficit had been reduced to 102 before Visée became Rankin’s fifth victim.
Rankin finished with five for 49, with two apiece for Murtagh and Mulder.
Ireland suffered an early setback when they batted again, Joyce caught by substitute Fred Klaassen off Van Beek’s bowling, but then Porterfield and Balbirnie shared a second-wicket partnership of 113 in 31 overs.
Porterfield had two notable strokes of good fortune: one when, on 44, he survived a sustained appeal for a catch in the gully which was turned down, the other six runs later when, having reached his second half-century of the match, he was put down at midwicket off O’Dowd’s bowling.
With Peter Borren off the field with an injured finger Wesley Barresi had taken over the captaincy, and when the total had reached 116 he elected to try his own occasional off-spin.
He was almost immediately successful, first bowling Balbirnie for a 94-ball 50 and then dismissing Gary Wilson in the same way. In between, Quirijn Gunning’s excellent performance in both innings had at last been rewarded with a wicket, John Anderson edging him through to keeper Visée.
Three wickets had fallen for 14 runs in the space of just 13 deliveries, but the lead was now 241, and Porterfield and Kevin O’Brien added another 28 by the close, the former moving onto 89.
The initial issue on Friday will be how long the Irish captain decides to bat on before setting the Dutch a target and giving his bowlers the opportunity to bowl the opposition out and complete the outright victory Ireland need to stay in touch with rivals Afghanistan.