Back-to-back defeats have seen Benfica's lead at the summit slashed to four points, while Estoril find themselves three points clear of the drop zone at the opposite end of the table.
Match preview
It looked as if Benfica would get their hands on the Primeira Liga trophy with several games to spare, but a recent downturn in form - and persistent pressure from Porto and Braga - means that the title race is set to go down to the wire.
After winning 12 of their opening 13 matches, the Eagles racked up 10 consecutive victories to open up a seemingly unassailable lead atop the standings, but they now find themselves just four points clear of second-placed Porto.
In fact, Porto became the first visiting side this season to win a Primeira Liga match at the Estadio da Luz when they claimed a 2-1 victory earlier this month, before Chaves inflicted a third league defeat of the campaign on Benfica.
Roger Schmidt's men played out a thrilling 3-3 draw with Inter Milan in the Champions League quarter-finals on Wednesday, following a 2-0 defeat in the first leg, so they enter Sunday's clash on a four-game winless run in all competitions.
Still, it is not all doom and gloom for Benfica, as they have won 23 of their 28 league encounters this term, and they will be confident of adding another victory to their tally when lowly Estoril Praia visit the Estadio da Luz.
While Benfica have taken 71 points from a possible 84 this season, Estoril Praia have managed to pick up just 25 points, losing 17 of their 28 Primeira Liga clashes along the way.
The Canaries parted company with manager Nelson Verissimo in February due to a run of eight losses in 10 matches, appointing Ricardo Soares as his successor, but the new boss has failed to turn the tide since his arrival.
Soares has lost six of his seven games in charge, meaning that Estoril have lost 14 of their previous 17 league outings, so they can count themselves fortunate to have remained out of the bottom three up to now.
Having lost each of their last eight away league games - scoring a measly four goals in the process - Estoril will need to up their output on the road if they want to steer clear of relegation trouble.
When you look at the bigger picture, the Canaries have only managed to score 11 goals in 14 away league matches this season, so they will struggle to breach the strongest defence in the division, regardless of Benfica's form.
Benfica Primeira Liga form:
W
W
W
W
L
L
Benfica form (all competitions):
W
W
L
L
L
D
Estoril Praia Primeira Liga form:
L
L
L
W
L
L
Team News
Having missed the past three games due to a knee issue, Benfica defender Alexander Bah is not expected to feature on Sunday, while German midfielder Julian Draxler remains sidelined with an ankle injury.
Fredrik Aursnes could continue on the left side of midfield after scoring against Inter in midweek, while Joao Mario will look to enhance his tally of 23 goals and 12 assists.
Veteran defender Nicolas Otamendi is likely to partner teenage prodigy Antonio Silva at centre-back, with Alex Grimaldo and Gilberto occupying the full-back roles.
Meanwhile, Estoril Praia will be without Brazilian defender Lucas Africo this weekend as the 28-year-old continues to recover from injury.
Benfica loanee Tiago Gouveia, who has bagged five goals and five assists this season, is unable to face his parent club, so Juventus loanee Alejandro Marques will lead the line on Sunday.
Benfica possible starting lineup:
Vlachodimos; Gilberto, Silva, Otamendi, Grimaldo; Luis, Chiquinho; Mario, Silva, Aursnes; Ramos
Estoril Praia possible starting lineup:
Figueira; Santos, Alvaro, Vital, Joaozinho; Ndiaye; Cassiano, Marques, Carvalho, Eduardo; Marques
We say: Benfica 4-1 Estoril Praia
This clash provides Benfica with the ideal opportunity to return to winning ways and reignite their title charge, so we expect the Eagles to soar to a comfortable victory on home soil.