Hastings came on for full-back Blair Kinghorn after 30 minutes against Wales, and impressed despite playing out of position, supplying the scoring pass for wing Darcy Graham's second-half try.
The second half did not see much action until the final six minutes when Chloe Rollie's try gave Scotland a 15-10 lead and a glimmer of hope for their first win in the tournament.
The former Ireland coach praised his players for the resilience they showed at the end of their hard week and for a superb second-half defensive effort helping them to protect most of the advantage they gained through first-half tries from winger Josh Adams and centre Jonathan Davies.
He has been joined on the sidelines by Seymour, who suffered a rib injury against Wales on Saturday, and Kinghorn who sustained an ankle problem in the same game.
Things were soon looking bleak for the hosts, who lost Seymour and Kinghorn either side of Davies rounding off a superb 24-phase move to extend Wales' lead, after Russell and Gareth Anscombe had exchanged three-pointers.
They have have been hit with a few injuries following the loss to Wales last weekend.
"We have got a dream at the moment and we will start planning for next week".
"We talked at the break about being pretty comfortable and going out to deliver a second-half (performance)".
From an attacking lineout, Gilchrist was held up over the line by Parkes.
And their pressure was rewarded through a fine 58th-minute score for Graham, which owed everything to smart creative work by Russell and replacement Byron McGuigan and concluded a dominant Scottish third quarter that saw Wales' penalty count stack up.
"Any team that's won a Grand Slam, and I think back even to a year ago with Ireland and that Johnny Sexton drop goal, you look back at certain games and know you've had a little bit of luck", said Gatland, on the verge of his third Grand Slam.
But despite the late surge, Scotland was unable to land the final blow and Wales finished off with a penalty in the final minute.