The on-loan striker, who had not been playing for Championship side Leeds, must have awaken many clubs to his immense ability as he not only scored seemingly at will, but also laid on a number of other chances which weren't taken.
It was Walsall's best home performance of the season, boosted by other on-loan players Craig Pead from Coventry and Southampton's young midfielder Andrew Surman.
Hull looked a shadow of the team that secured promotion last week and still have hopes of finishing the season as League One champions.
Almost from the start Walsall were by far the more active, determined and effective side, although their goalkeeper Andy Oakes did have to make a couple of early saves from Ian Ashbee and Nick Barmby.
But it was Hull goalkeeper Boaz Myhill who had to pull off the first really outstanding save by flinging himself to his left to keep out a fierce 14 minute drive from Surman.
That set the pattern for the rest of the match as Walsall constantly moved forward with the opening goal coming after 34 minutes.
David Perpetuini sent over a telling low cross from the left and Joachim used all of his pace to race in and beat Myhill with a low shot.
Both Michael Standing and Surman missed chances for Walsall before half time, but they deservedly increased the lead in the 53rd minute.
Surman saw a shot blocked and Joachim, quick to see the opportunity, took possession to leave Myhill no chance with a low shot into the far corner.
Hull's cause was not helped when they lost injured skipper Ashbee in the 54th minute, although his replacement Andy Hessenthaler came on to show a lot of experience.
However, it was virtually all Walsall and it was not surprising when they increased the lead inevitably through Joachim after 68 minutes.
A long clearance was missed by Hull defender Damien Delaney and with Myhill advancing well of his line, Joachim was able to send a low angled shot into an empty net.
Walsall could have gone further in front six minutes from the end but Myhill made a fine save from Surman's header.