Mayor Bill de Blasio and NYPD brass bowed their heads alongside Mets fans Monday at Citi Field to honor slain detectives Rafael Ramos and Wenjian Liu during a moment of silence at the home opener.

Family members of Ramos and Liu -- gunned down Dec. 20 as they sat in their patrol car in the Bedford-Stuyvesant section of Brooklyn -- threw out the ceremonial first pitch. They donned Mets jerseys with the names "Ramos" and "Liu" emblazoned across the back.

The crowd cheered loudly for Ramos and Liu when the announcer noted that the partners were posthumously promoted to the rank of detective.

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Members of the NYPD sang the national anthem and presented the colors at the ceremony. The police department's aviation unit conducted a flyover of the stadium, with three helicopters streaking overhead through the clear sky. NYPD Deputy First Commissioner Benjamin Tucker was among the department officials who attended and greeted the family.

Ramos' young sons, Jaden and Justin, and Liu's widow, Pei Xia Chen, threw ceremonial first pitches to the Mets' David Wright, Matt Harvey and Curtis Granderson. Ramos' widow, Maritza, and Liu's mother and father were also in attendance.

"We are so happy to be here," Chen said before the game. She thanked the Mets for their support of the families. "Let's go, Mets."

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Among other gestures, Wright called Jaden and Justin Ramos in the wake of their father's slaying. Jaden visited Wright and the Mets at spring training.

"We're grateful for everything the Mets have done for us, and I just wish my husband was here to see it because he was a big Mets fan," Maritza Ramos said.

Ramos, 40, and Liu, 32, were killed by a gunman who expressed anti-police sentiments on social media and condemned the July 2014 NYPD-involved death of Staten Island man, Eric Garner. Ismaaiyl Brinsley, 28, shot and wounded his girlfriend in Maryland before he shot the officers and ultimately killed himself at a nearby subway station in Brooklyn.

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De Blasio, criticized last year by the Patrolmen's Benevolent Association and others as unsupportive of the NYPD, was booed by some members of the crowd when his name was announced. He did not react, nor did he comment after the ceremony.

At the hospital the night of Ramos and Liu's deaths and at both funerals, critics of the mayor, including uniformed members of the NYPD and other police departments, turned their backs to the mayor in silent protest. Tensions have since eased.