Liverpool maintained their pursuit of Champions' League qualification as Riise scored his sixth of the season to secure Liverpool's fourth away league win of a fluctuating campaign at Charlton Athletic, with a 2-1 victory. But the 20-yard equaliser by Morientes was met with equal relief and delight following the Spanish striker's struggle for fitness and goals in his first three matches for the club.
"There was some pressure on him because of his reputation and all the talk about him before he came," Riise said. "But he is a really nice guy, so easy to talk to and he works well in training. He was always going to need time to get used to the Premiership. He has shown in training what a good finisher he is and he proved that against Charlton. There is a lot more to come and we are looking forward to it."
When Morientes signed for Liverpool in a pounds 6m deal from Real Madrid, he had not played a full match since last season's Champions' League final while on loan at Monaco. That lack of match practice sparked criticism that he was not the right man to revive Liverpool's campaign.
But Riise believes Morientes can help Liverpool achieve their Champions' League ambitions.
Riise said: "His reputation is good and he came here because he wants to score goals and win trophies with Liverpool.
"When he arrived it said to everybody that this team is going upwards and is going to win trophies, and that is why all the players are working together. We are in one final (the Carling Cup), but want to do better. The Champions' League is starting up again soon, so we are looking forward to that."
Liverpool's win at The Valley meant they avoided a third successive league defeat, and Riise added: "The Charlton win was our best performance away from home of the season. We knew that after playing three or four games not that well lately, it was a must-win for us, especially when [close rivals] Tottenham and Middlesbrough lost as well."
Alan Curbishley is hoping Charlton do not run out of steam as they attempt to secure a top-six finish.
While Middlesbrough were beaten at Portsmouth, Bolton's win over Tottenham saw them climb back into contention, just a point behind Charlton, who remain seventh on goal difference. To be competing for at least a Uefa Cup place is an achievement in itself for Charlton, who attracted a bumper 27,102 crowd on Tuesday night, the biggest since they returned to The Valley.
However, with three successive away games now on the cards - at Newcastle United, Middlesbrough and Fulham - Curbishley is all too aware that the next month could well shape Charlton's campaign.
"It has been a great achievement so far," Curbishley said. "We normally run out of steam and don't quite finish it off, although last year I was delighted to have come seventh. If we come anywhere around there, then I will be delighted again.
"But there is a third of the season left and the way the fixtures have been thrown out, we have got a tough period coming up, so I think the next month is an important time for us."
While Curbishley was gracious in defeat, he was left to reflect on the talent available to his Anfield counterpart Rafael Benitez, despite the current spate of injuries which have hampered the Liverpool manager's team selections.
"You don't want to go into finances and things like that, but the top four clubs, and we know who they are, that is how it is going to end up most years," the Charlton manager said. "Sometimes someone comes along to upset that, and it might be Everton this year.
"Liverpool have had a lot of injuries, and they can still put a team out like that - I think that's the difference between them and the rest of the Premiership."