Saracens, who came into Saturday's match on the back of their club record 68-10 loss away to Bath, ended Bristol's 10-game winning streak on the road with Willis leading the way in a bonus-point success.
Both of his tries showcased the 25-year-old's power, while rising star Willis's second score also featured impressive pace and footwork as he evaded three tacklers while surging down the right wing.
Red Rose boss Steve Borthwick has so far resisted calls to cap Willis but the back-row forward's latest display will have done his cause no harm ahead of England's Six Nations opener away to champions Ireland on February 1st.
"Tom was outstanding and he's been outstanding all season," said McCall, adding: "He just needs to keep on doing what he's doing. If he keeps putting in performances like this, I think he will get rewarded in the end."
Fergus Burke also scored two tries for Saracens, with Lucio Cinti going over as well, as the team marked England captain Jamie George's 300th appearance for the London club in style.
Victory saw Saracens close to within a point of second-placed Bristol as the southwest side suffered a second straight league defeat following last week's shock 38-0 thrashing by Sale.
It was a different story for Sale as Wales scrum-half Tomos Williams showed his Test class with two of Gloucester's five tries in a 36-20 win over the Sharks.
Leicester denied Exeter a first away win in the league this season, the Tigers prevailing 28-15.
Exeter rallied from 14-3 behind at half-time to lead 15-14 before losing Will Rigg to the sin-bin for what was deemed to be an illegal challenge on England full-back Freddie Steward.
Leicester capitalised on their man advantage by scoring two converted tries in Rigg's absence, with Exeter left second bottom after a ninth defeat in 10 league games.
Exeter boss Rob Baxter was left frustrated by the television match official's role in Rigg's sin-binning.
"The referee (Christophe Ridley) was right on the spot and his original assessment was just a knock-on, but then the TMO gets involved and the incident was upgraded to a yellow card," said Baxter, who also accepted Exeter had "dropped too many balls and were inaccurate".
Table-toppers Bath are away to struggling champions Northampton on Sunday in a repeat of last season's final.