DeSean Jackson’s speed got the 49ers’ attention last month.

After the 49ers’ 17-13 win over Washington, safety Eric Reid acknowledged a primary focus was limiting the field-stretching receiver, who leads the NFL in yards per catch (20.0) and receptions of 40-plus yards (10). Jackson finished with two catches for 39 yards against the 49ers.

“That was a huge part of our game plan,” Reid said. “Know where he was … He has the most 40-yard receptions in the NFL, so our game plan was to just to know where he was and get someone over the top of him.”

In search of speed, the 49ers, of course, expressed interest in Jackson before he signed with Washington. And they later explored trading up in the first round of the draft for Giants dynamic rookie Odell Beckham Jr., who is already commanding plenty of attention from defensive coordinators.

After missing out on Jackson and Beckham, the 49ers added another wideout on the second day of the draft by trading for Stevie Johnson, who averaged 11.5 yards a catch in 2013. Johnson joined a wide receiver corps that included Anquan Boldin, Michael Crabtree and Brandon Lloyd, who was signed in April.

The additions of Johnson and Lloyd gave the 49ers a quartet of wideouts who each had at least one 1,000-yard season since 2010.

The problem? None of those receivers inspire opponents to create we’ve-got-to-stop-him game plans. Consider that the 34-year-old Boldin averages a team-high 12.4 yards per catch, which is the third-lowest team-leading figure in the NFL (Jets, Dolphins).

In addition, despite possessing a rocket-armed quarterback in Colin Kaepernick, the 49ers have four pass plays of 40-plus yards, which is tied for the fourth-lowest total in the NFL.

Former NFL quarterback Chris Simms pointed to the lack of outside speed when assessing some of Kaepernick’s struggles this season.

“The talent around him, you look at the receivers – Michael Crabtree, Stevie Johnson, Anquan Boldin – they are not game-breakers,” Simms said on “NFL Monday QB” on the CBS Sports Network. “Those are names and names only. They are not keeping defensive coordinators up late at night. (Opponents) are not worried about how they’re going to stop Michael Crabtree.”

Of course, it also hasn’t helped Kaepernick’s cause that tight end Vernon Davis is in the midst of a season-long disappearing act. Davis (23 catches, 210 yards) is averaging 9.1 yards a reception and has one reception of at least 20 yards (matching the total of Steelers cornerback Antwon Blake). Last year, Davis had 52 catches, averaged 16.3 yards a reception and had 16 catches of at least 20 yards.

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Teams with fewest completions of 40-plus yards (13 players have at least four catches of 40-plus yards):

T26. 49ers, 4

T26. Panthers, 4

T26. Jets, 4

T26. Raiders, 4

30. Vikings, 2

31. Dolphins, 1

32. Chiefs, 0

Twitter: @Eric_Branch