The duo, both signed during the January transfer window, shone as their burgeoning partnership helped Hull to a third away league win of the season.
Jelavic stole the headlines with his double sandwiched by goals from Tom Huddlestone and Jake Livermore.
However, Long was no less important as his typical industry came amid some wonderful link-up play with his strike partner.
Bruce, who earned his 100th Premier League win, said: "I didn't think we played particularly well in the first half; we gave the ball away a little bit too cheaply.
"But what has got us the win is that little bit of quality we have invested in up the top end of the pitch.
"When you are not playing very well, if you've got two like we have then you are a threat. And certainly the second goal, in particular, they made it out of nothing. The link-up play was there for all to see.
The former Sunderland manager feels that his negotiation of the January market represented money well-spent with his newfound forward duo showing the value of elite-level experience.
"That was the difference, the ability to score a goal and with these two in the team, we have all of a sudden got it," Bruce continued.
"The two of them have a great appetite for the game and work ethic. They are a handful; with the pace of Long and the physical presence Jelavic gives you, with a turn of pace too, they are a handful for any defence."