Bump for DiaconoGuillermo... I'm curious to hear your answer.
I was hoping that we might get more information before I wrote a response. In is absence I can only offer some speculation. Given that Sunday was Pentecost I doubt that any priest would omit any essential rite of the Mass, most particularly the Penitential rite. That being said there are three ordinary Penitential rites from which he might choose.
A) All may say
I Confess to almighty God....
Then the priest says the absolution
B) The priest Says
Lord, we have sinned against you
Lord, have mercy
The people answer
Lord, have mercy
Priest
Lord, show us your mercy and love.
People
And grant us your salvation.
The priest says the absolution
C) The priest says
An invocation
Lord, have mercy
The people answer
Lord, have mercy
Priest
An invocation
Christ, have mercy
People
Christ, mercy
Priest
An invocation
Lord, have mercy
People
Lord, have mercy
The priest says the absolution
It has been my experience that rite B is the least often used and rite C is the most often used in English speaking communities while rite A is the most often used in Hispanic communities,
The Penitential Rite is not used if the Sprinkling Rite is used, especially during the Mass on the Vigil of Easter (required). This rite can be optionally used at any Mass and, my parish at least, it is commonly used during the Season of Easter.
If the Mass incorporates the Sacrament of Baptism the public renunciation of sin from the Rite of Baptism may replace the penitential rite and the declaration of faith from the same rite my stand in the stead of the Creed.
It should be noted that in these two cases for pastoral reasons they may come after the Homily rather than before (again see the Liturgy of the Vigil of Easter as the prototype). Finally note that Pentecost is a much favored day for Baptism of infants in many communities.