A goal surrendered off a set piece and another blown second-half lead were the difference Wednesday as the Portland Timbers salvaged a 2-2 draw with Toronto.
Darlington Nagbe headed home the equalizer in the 82nd minute after Eric Hassli and Luis Silva gave Toronto a 2-1 advantage with two quick goals in the second half.
But it was Sal Zizzo's opener off a corner kick in the 21st minute that had Mariner fuming as Toronto again surrendered a goal off a dead-ball situation.
"It's the players' fault. You've got to execute," said Mariner, who is 4-4-5 since taking over for Aron Winter. "You look at the setups. Every single team in the world sets up slightly differently but the No. 1 thing you've got to do is to have that desire inside of you that that ball is not going to be won by one of the opposition. Cleanly. Can't happen. And if it does, then you've got to react and get the ball out of your box and it's something that we have difficulty dealing with."
Toronto (5-13-5) is now winless in three and still sits last in the overall standings, a point back of Portland (5-12-6).
"We've come to expect a standard and we let that standard slip. Giving away another set piece, it's lazy in a way," Toronto FC defender Richard Eckersley said. "I just think you've got to have the willingness to go and win the ball. If you get anything on it just get it away and at the minute I don't think we have that."
Added Toronto FC goalkeeper Milos Kocic: "That's probably the weakest part of our team — the set pieces."
Trailing 1-0 at the half, Toronto changed its tactics after a dismal showing and saw immediate dividends in grabbing the lead.
"We needed a shakeup at halftime. Everybody in the stand saw that and everybody watching at home on television saw that," Mariner said. "They responded extremely well. Came out of the blocks very very quick."
Hassli, making his first appearance at BMO Field since being acquired from Vancouver last month, tied the score in the 57th minute on a rebound off a shot from Silva.
Hassli was mobbed by his teammates before running to the sidelines to hug Mariner.
Toronto then grabbed the lead in the 63rd when Silva buried a flick on from Hassli past Portland goalkeeper Donovan Ricketts.
"You can see what Eric Hassli brings to the table," Mariner said. "He's such an immense presence on the field."
Despite the positives up front, a makeshift TFC defence that was missing five regulars because of international duty, suspension and injury, looked sloppy for most of the night.
The Toronto back four was without newly-signed defender Darren O'Dea (Ireland), Dicoy Williams (Jamaica) and Doneil Henry (Canada), who were with their respective national teams. Add to that Logan Emory's suspension and Jeremy Hall's ankle injury and Mariner was left with few options.
The former England international implored his players to keep it simple in defence as Adrian Cann saw his first MLS action since June 16 because of a knee injury, while the out-of-favour Ty Harden played in the league for the first time since April 7.
But things looked shaky from the outset as Portland carried the play for large chunks of the game.
"Anybody who has played the game knows full well that you can train your backside off but as soon as that whistle goes, the tempo is totally different," Mariner said. "The level is different, the whole energy is different."
The Timbers nearly doubled their first-half lead in the 50th minute when Zizzo's free kick from the left flashed just wide of Kocic's goal.
After TFC took a 2-1 lead, Portland striker Chris Boyd found himself in alone on Kocic in the 70th minute, but the Toronto FC goalkeeper came up with a big save.
Although the defence was Mariner's main concern coming into the match, Toronto FC was also without midfielder Terry Dunfield (Canada) and forward Ryan Johnson (Jamaica) because of international callups.
Toronto FC has never made the MLS playoffs but with another season seemingly lost, Mariner remained positive.
"How many teams in MLS can have five starters out and put in a performance like that?" he asked. "We're nowhere near where we want to be but I'm delighted with camaraderie, the togetherness that is in that locker-room."
Notes: Toronto FC midfielder Reggie Lambe was substituted in the second half because of a knee injury. ... Toronto FC midfielder Aaron Maund made the first MLS start of his career. ... Ricketts made his Portland debut after coming over in a trade with Montreal last week. ... Toronto FC's next game is Saturday at home against Sporting Kansas City. ... Portland is at New York on Sunday. ... Toronto midfielder Matt Stinson (quadriceps strain) did not play and is expected to miss up to a month. ... Toronto striker Danny Koevermans underwent surgery to repair his injured left knee in Toronto on Tuesday. The Dutchman tore his anterior cruciate ligament against New England last month and isn't expected back until next May. ... Attendance was 18,773.